Nanosensors and related technologies

ABSTRACT

The present invention generally relates to nanoscale wire devices and methods for use in determining nucleic acids or other analytes suspected to be present in a sample. For example, a nanoscale wire device can be used to detect single base mismatches within a nucleic acid (e.g., by determining association and/or dissociation rates). In one aspect, dynamical information such as a binding constant, an association rate, and/or a dissociation rate, can be determined between an analyte and a binding partner immobilized relative to a nanoscale wire. In some cases, the nanoscale wire includes a first portion comprising a metal-semiconductor compound, and a second portion that does not include a metal-semiconductor compound. The binding partner, in some embodiments, is immobilized relative to at least the second portion of the nanoscale wire, and the size of the second portion of the nanoscale wire may be minimized and/or controlled in some instances.

RELATED APPLICATIONS

This application is a national phase filing under 35 U.S.C. §371 ofInternational Application No. PCT/US2007/013700, filed Jun. 11, 2007,entitled “Nanosenors and Related Technologies” by Leiber, et al., whichclaims the benefit of U.S. Provisional Patent Application Ser. No.60/812,884, filed Jun. 12, 2006, entitled “Nanosensors and RelatedTechnologies,” by Lieber, et al., both of which are incorporated hereinby reference in their entirety.

GOVERNMENT FUNDING

This invention was made with government support under Grant Nos.FA8650-06-C-7622, FA9550-05-1-0279, and N66001-04-1-8903 awarded byDARPA. The government has certain rights in the invention.

FIELD OF INVENTION

The present invention generally relates to nanotechnology andsub-microelectronic circuitry, as well as associated methods anddevices, for example, nanoscale wire devices and methods for use indetermining nucleic acids or other analytes suspected to be present in asample (for example, their presence and/or dynamical information), e.g.,at the single molecule level. For example, a nanoscale wire device canbe used to detect single base mismatches within a nucleic acid (e.g., bydetermining association and/or dissociation rates). In some cases, thedevices may include metal-semiconductor compounds, such as metalsilicides.

BACKGROUND

Interest in nanotechnology, in particular sub-microelectronictechnologies such as semiconductor quantum dots and nanowires, has beenmotivated by the challenges of chemistry and physics at the nanoscale,and by the prospect of utilizing these structures in electronic andrelated devices. Nanoscopic articles might be well-suited for transportof charge carriers and excitons (e.g. electrons, electron pairs, etc.)and thus may be useful as building blocks in nanoscale electronicsapplications. Nanowires are well-suited for efficient transport ofcharge carriers and excitons, and thus are expected to be importantbuilding blocks for nanoscale electronics and optoelectronics.

Nanoscale wires having selectively functionalized surfaces have beendescribed in U.S. patent application Ser. No. 10/020,004, entitled“Nanosensors,” filed Dec. 11, 2001, published as Publication No.2002/0117659 on Aug. 29, 2002, and in corresponding International PatentApplication Serial No. PCT/US01/48230, filed Dec. 11, 2001, published asInternational Patent Application Publication No. WO 02/48701 on Jun. 20,2002 (each incorporated herein by reference). As described,functionalization of the nanoscale wire may permit interaction of thefunctionalized nanoscale wire with various entities, such as molecularentities, and the interaction induces a change in a property of thefunctionalized nanowire, which provides a mechanism for a nanoscalesensor device for detecting the presence or absence of an analytesuspected to be present in a sample.

SUMMARY OF THE INVENTION

The present invention generally relates to nanotechnology andsub-microelectronic circuitry, as well as associated methods anddevices, for example, nanoscale wire devices and methods for use indetermining nucleic acids or other analytes suspected to be present in asample (for example, their presence and/or dynamical information), e.g.,at the single molecule level. For example, a nanoscale wire device canbe used to detect single base mismatches within a nucleic acid (e.g., bydetermining association and/or dissociation rates). The subject matterof the present invention involves, in some cases, interrelated products,alternative solutions to a particular problem, and/or a plurality ofdifferent uses of one or more systems and/or articles.

The invention is a method in one aspect. In one set of embodiments, themethod includes an act of determining a binding constant and/or adissociation rate constant between a nucleic acid and a nanoscale wirehaving immobilized relative thereto a binding partner of the nucleicacid. In another set of embodiments, the method includes an act ofdetermining a binding constant and/or a dissociation rate constantbetween an analyte and a nanoscale wire having a binding partner of theanalyte immobilized relative thereto.

The method, in still another set of embodiments, includes acts ofproviding a plurality of nucleic acid molecules, each associated with arespective binding partner immobilized relative to a nanoscale wire,dissociating at least some of the plurality of nucleic acid moleculesfrom the respective binding partners, and determining a rate at whichthe at least some of the plurality of nucleic acid molecules dissociatefrom the respective binding partners.

According to yet another set of embodiments, the method comprises actsof diffusing at least a portion of a metal into a first portion of ananoscale wire but not into a second portion of the nanoscale wire, andimmobilizing a reaction entity to a second portion of the nanoscalewire.

In still another set of embodiments, the method includes acts ofproviding a bulk metal adjacent a semiconductor wire, and diffusing atleast a portion of the bulk metal into at least a portion of thesemiconductor wire in a longitudinal direction along the semiconductorwire for a distance of at least about 10 nm.

According to yet another embodiment, the method includes an act ofdetermining a number of mismatches between an analyte nucleic acid and abinding partner nucleic acid immobilized relative to a binding partnerof the nucleic acid.

In another aspect, the invention is an article. The article includes, inone set of embodiments, a nanoscale wire comprising a first portioncomprising a metal silicide, and a reaction entity immobilized relativeto a second portion of the nanoscale wire having a composition differentfrom the first portion. In another set of embodiments, the articleincludes a nanoscale wire comprising a first portion comprising a metalsilicide, and a second portion having a composition different from thefirst portion. In some cases, the second portion has a greatestdimension no greater than about 100 nm.

The article, in yet another set of embodiments, includes a nanoscalewire comprising a first portion and a second portion, where the firstportion has a binding partner immobilized relative thereto. In someinstances, the second portion is free of the binding partner.

Still another aspect of the invention is generally directed to asolution. In some embodiments, the solution includes an analyte, and ananoscale wire comprising a first portion and a second portion. Thesecond portion may have immobilized relative thereto a binding partnerto the analyte, and the first portion may be free of the bindingpartner. In one embodiment, the analyte has a Debye screening lengthgreater than the greatest dimension of the second portion of thenanoscale wire.

In another aspect, the present invention is directed to a method ofmaking one or more of the embodiments described herein, for example, asensing device comprising a nanoscale wire. In yet another aspect, thepresent invention is directed to a method of using one or more of theembodiments described herein, for example, a sensing device comprising ananoscale wire.

Other advantages and novel features of the present invention will becomeapparent from the following detailed description of various non-limitingembodiments of the invention when considered in conjunction with theaccompanying figures. In cases where the present specification and adocument incorporated by reference include conflicting and/orinconsistent disclosure, the present specification shall control. If twoor more documents incorporated by reference include conflicting and/orinconsistent disclosure with respect to each other, then the documenthaving the later effective date shall control.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting embodiments of the present invention will be described byway of example with reference to the accompanying figures, which areschematic and are not intended to be drawn to scale. In the figures,each identical or nearly identical component illustrated is typicallyrepresented by a single numeral. For purposes of clarity, not everycomponent is labeled in every figure, nor is every component of eachembodiment of the invention shown where illustration is not necessary toallow those of ordinary skill in the art to understand the invention. Inthe figures:

FIGS. 1A-1E are schematic diagrams illustrating various embodiments ofthe invention;

FIGS. 2A-2K are schematic diagrams illustrating various techniquesuseful in the fabrication of certain embodiments of the invention;

FIGS. 3A-3G illustrate the determination of the association/dissociationof nucleic acid molecules to binding partners at differentconcentrations, according to one embodiment of the invention;

FIGS. 4A-4G illustrate the determination of kinetics of association anddissociation of an analyte with a binding partner, in one embodiment ofthe invention;

FIG. 5 illustrates the determination of multiple associations ofindividual nucleic acid molecules to binding partners, according to someembodiments of the invention;

FIGS. 6A-6B illustrate sensors according to various embodiments of theinvention; and

FIG. 7 is a schematic diagram of one embodiment of the invention.

BRIEF DESCRIPTION OF THE SEQUENCES

SEQ ID NO: 1 is ATCATCTTTG, a synthetic PNA sequence;

SEQ ID NO: 2 is CAAAGATGAT, a synthetic DNA sequence;

SEQ ID NO: 3 is CAAACATGAT, a synthetic DNA sequence;

SEQ ID NO: 4 is CAAACCTGAT, a synthetic DNA sequence;

SEQ ID NO: 5 is ATCAAAGATG, a synthetic DNA sequence;

SEQ ID NO: 6 is TTTTTTTTTT, a synthetic DNA sequence;

SEQ ID NO: 7 is CAAAGATG, a portion of SEQ ID NO: 5; and

SEQ ID NO: 8 is CATCTTTG, a portion of SEQ ID NO: 1.

DETAILED DESCRIPTION

The present invention generally relates to nanotechnology andsub-microelectronic circuitry, as well as associated methods anddevices, for example, nanoscale wire devices and methods for use indetermining nucleic acids or other analytes suspected to be present in asample (for example, their presence and/or dynamical information), e.g.,at the single molecule level. For example, a nanoscale wire device canbe used in some cases to detect single base mismatches within a nucleicacid (e.g., by determining association and/or dissociation rates). Inone aspect, dynamical information such as a binding constant, anassociation rate, and/or a dissociation rate, can be determined betweena nucleic acid or other analyte, and a binding partner immobilizedrelative to a nanoscale wire. In some cases, the nanoscale wire includesa first portion comprising a metal-semiconductor compound, and a secondportion that does not include a metal-semiconductor compound. Thebinding partner, in some embodiments, is immobilized relative to atleast the second portion of the nanoscale wire, and the size of thesecond portion of the nanoscale wire may be minimized and/or controlledin certain instances. Articles and devices of size greater than thenanoscale are also included in some embodiments. Still other aspects ofthe invention include assays, sensors, kits, and/or other devices thatinclude such nanoscale wires, methods of making and/or using suchnanoscale wires, or the like.

One aspect of the invention is generally directed to determiningdynamical information, for example, a binding constant, and/or anassociation and/or a dissociation rate constant between an analyte, suchas a nucleic acid, and a nanoscale wire having immobilized relativethereto a binding partner to the analyte. The nanoscale wire may be (orcomprise), for example, a nanotube or a nanowire, e.g., a semiconductornanowire, a metal nanowire, a metal-semiconductor nanowire (e.g., ametal silicide nanowire), etc., as discussed in greater detail below. Inone set of embodiments, the analyte (i.e., the substance to bedetermined using the nanoscale wire) is a nucleic acid, for example,DNA, RNA, PNA, or the like, as well as combinations thereof. The bindingpartner may also be a nucleic acid that is substantially or perfectlycomplementary to the analyte nucleic acid. However, in otherembodiments, binding partners other than nucleic acids may be used (forexample, an enzyme able to recognize the analyte nucleic acid), asdescribed below. The nanoscale wire may also have a plurality of bindingpartners immobilized relative thereto, which may each independently bethe same or different (e.g., multiple, substantially identical copies ofthe same nucleic acid sequence, and/or different nucleic acid sequences,and/or combinations thereof). In some embodiments, the analyte can bedetermined with a high degree of sensitivity, and in some cases even asingle molecule of analyte can be determined.

A nucleic acid typically has a plurality of bases, connected via apolymer backbone. Non-limiting examples of nucleic acids include RNA(ribonucleic acid), DNA (deoxyribonucleic acid), or PNA (peptide nucleicacid). Typically, a nucleic acid includes multiple nucleotides, forexample, adenosine (“A”), guanosine (“G”), thymine (“T”), uridine (“U”),or cytidine (“C”). Nucleotides often are formed from moleculescomprising a sugar (e.g. ribose or deoxyribose) linked to a phosphategroup and an exchangeable organic base (although a PNA has a differentbackbone, i.e., one comprising peptide linkages). A sugar (or peptide)and a base (without the phosphate) together form a nucleoside. Examplesof organic bases include, but are not limited to, various pyrimidines orpurines.

In one set of embodiments, the binding partner is a nucleic acid (orcontains a nucleic acid sequence) that is substantially or perfectlycomplementary to the analyte nucleic acid (or a portion thereof). Asused herein, a first portion of a nucleic acid is “complementary” to asecond portion of a nucleic acid if the nucleotides of the first portionand the nucleotides of the second portion are generally complementary(i.e., Watson-Crick pairing, A to T or U, C to G, etc.). Typically, thenucleic acids have enough complementarity that the nucleic acids areable to specifically bind together in a defined, predictableorientation. In some cases, the nucleic acid portions are at least 80%,at least 85%, at least 90%, at least 95%; at least 96%, at least 97%, atleast 98%, or at least 99% complementary. Perfectly complementarynucleic acids are 100% complementary. In some embodiments, the first andsecond portions have a maximum of 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10nucleotide mismatches, and in some instances the number of mismatchesbetween the nucleic acids may be determined, e.g., as discussed herein.A non-limiting example of nucleic acids having nucleotide mismatches areSNPs, or single nucleotide polymorphisms, which are well-known to thoseof ordinary skill in the art. The complementary portions of the nucleicacids may be at least 5 nucleotides in length, and in some cases, atleast 7 nucleotides in length, at least about 10 nucleotides in length,at least about 12 nucleotides in length, at least about 15 nucleotidesin length, at least about 20 nucleotides in length, at least about 25nucleotides in length, at least about 50 nucleotides in length, etc.

In some embodiments, association or binding of an analyte (e.g., anucleic acid) to a binding partner may alter a property of the nanoscalewire, for example, an electrical property such as the conductivity ofthe nanoscale wire, e.g., if the analyte is charged. As a non-limitingexample, a negatively charged analyte, such as a nucleic acid, that toassociates with a binding partner and becomes immobilized with respectto a p-type nanoscale wire may increase the conductance of the p-typenanoscale wire (or decrease the conductance of an n-type nanoscalewire). Similarly, a positively charged analyte would increase theconductance of an n-type nanoscale wire, or decrease the conductance ofa p-type nanoscale wire. Such conductance changes are typicallyreversible, i.e., if the analyte subsequently dissociates or unbindsfrom the binding partner, the nanoscale wire generally returns to itsoriginal conductance. A determination of the conductivity or otherproperty of the nanoscale wire, and/or a change in such conductivity orother property can thus allow determination of the association and/ordissociation of the analyte with the binding partner.

In one embodiment, a conductance (or a change in conductance) of lessthan about 1 nanosiemens (nS) in a nanoscale wire sensor of theinvention can be detected. In another embodiment, a conductance in therange of thousandths of nS can be detected. In other embodiments,conductances of less than about 10 microsiemens, less than about 1microsiemens, less than about 100 nS, or less than about 10 nS can bedetected. The concentration of a species, or analyte, may be detectedfrom femtomolar concentrations, to nanomolar, micromolar, millimolar,and to molar concentrations and above. By using nanoscale wires withknown detectors, sensitivity can be extended to single molecules in somecases, as discussed herein. As a non-limiting example, differencesbetween a first nucleic acid (such as DNA) and a second nucleic acidhaving a difference of a single base may be determined using certainembodiments of the invention, e.g., at the single molecule level, asdiscussed in more detail below.

As another non-limiting example, a charged analyte, such as a nucleicacid, may be determined by determining a change in an electricalproperty of the nanoscale wire, for example, voltage, current,conductivity, resistivity, inductance, impedance, electrical change, anelectromagnetic change, etc. Immobilizing a charged analyte relative tothe nanoscale wire may cause a change in the conductivity of thenanoscale wire, and in some cases, the distance between the chargedanalyte and the nanoscale wire may determine the magnitude of the changein conductivity of the nanoscale wire.

In certain cases, additional properties of an analyte may be determinedbased on the association of the analyte with the binding partner. Forinstance, the rate of association and/or dissociation of the analyte tothe binding partner may be determined using the nanoscale wire. In somecases, a binding constant of the association may be determined. Thebinding constant is, generally speaking, a measure of the ratio betweenthe respective rates of association and dissociation of the analyte tothe binding partner.

As a non-limiting example, the analyte and the binding partner can eachbe nucleic acids (which can be of the same type, or of different types),and dynamical information, such as a binding constant, an associationrate, and/or a dissociation rate may be determined between the nucleicacids using the nanoscale wire. In certain embodiments, the bindingconstant and/or the dissociation rate may be sensitive to the number ofmismatches between the analyte nucleic acid and its binding partnernucleic acid. For example, if one or more mismatches are present, thenthe relative rates of dissociation may be substantially different,relative to perfectly complementary nucleic acids. Accordingly, evenrelatively small numbers of mismatches (e.g., 5 or less, 4 or less, 3 orless, 2 or less, or 1 or less) may be detected using various embodimentsof the invention, and in some cases, a single nucleotide mismatch of asingle molecule may be determined using a nanoscale wire of theinvention. Thus, in another aspect of the invention, a nanoscale wiremay be used to determine mismatches between two nucleic acids of theinvention, for example, between a first nucleic acid, immobilizedrelative to a nanoscale wire (or a portion thereof), and a secondnucleic acid (i.e., an analyte molecule) that is substantially orperfectly complementary to the first nucleic acid. Additionally, asdiscussed herein, in some cases, single nucleic acid molecules (i.e., afirst nucleic acid molecule and a second nucleic acid molecule) may bedetermined, including possible mismatches between the first and secondnucleic acid molecules.

The rates of association and/or dissociation, and/or the bindingconstant of the analyte with respect to the binding partner, and/or thedetermination of mismatches in complementary nucleic acids, may bedetermined using any suitable technique. In one set of embodiments, theconductivity of the nanoscale wire is measured as a function of time,for instance, by using the nanoscale wire within a field effecttransistor (“FET”) to measure conductivity. Those of ordinary skill inthe art will be aware of FETs and how to make and use them. Forinstance, an alternating current (“AC”) signal may be used through a FETin some instances to determine association and/or dissociation of ananalyte with a binding partner, for example, an AC signal having anamplitude of between 10 mV and 30 mV, and/or a frequency of between 17Hz and 500 Hz. The conductivity of the nanoscale wire may change indiscrete or measurable increments, corresponding to the associationand/or dissociation of individual analyte molecules to the bindingpartners immobilized with respect to the nanoscale wire, and suchchanges may be used to determine the rates of association and/ordissociation (or binding/unbinding). Typically, such rates arequantified using measures such as “rate constants” and similarparameters, as are known to those of ordinary skill in the art (e.g.,k_(on) and k_(off)).

Interaction of the analyte with the binding partner may cause adetectable change or modulation in a property of the nanoscale wire, forexample, through electrical coupling with the binding partner. The term“electrically coupled” or “electrocoupling,” when used with reference toan analyte and a binding partner, refers to an association between anyof the analyte, binding partner, and/or the nanoscale wire such thatelectrons can move from one to the other, or in which an electricalcharacteristic (or a change in the electrical characteristic) of one canbe determined by one of the others (e.g., through capacitance coupling,transient imbalances in ion concentration, or the like). This caninclude electron flow between these entities, or a change in a state ofcharge, oxidation, or the like, that can be determined by the nanoscalewire. As examples, electrical coupling or immobilization can includedirect covalent linkage between the analyte and the nanoscale wire,indirect covalent coupling (for instance, via a linker, and/or aplurality of linkers, e.g., serially), direct or indirect ionic bondingbetween the analyte and the nanoscale wire, direct or indirect bondingof both the analyte and the nanoscale wire to a particle (i.e., theparticle acts as a linker between the analyte and the nanoscale wire),direct or indirect bonding of both the analyte and the nanoscale wire toa common surface (i.e., the surface acts as a linker), and/or othertypes of bonding or interactions (e.g. hydrophobic interactions orhydrogen bonding). In some cases, no actual covalent bonding isrequired; for example, the analyte or other moiety may simply becontacted with the nanoscale wire surface. There also need notnecessarily be any contact between the nanoscale wire and the analyte orother moiety where the nanoscale wire is sufficiently close to theanalyte to permit electron tunneling or other effects between theanalyte and the nanoscale wire.

Thus, the binding partner may be immobilized relative to the nanoscalewire to cause a detectable change in the nanoscale wire. In some cases,the binding partner is positioned within about 100 nm of the nanoscalewire, within about 75 nm of the nanoscale wire, within about 50 nm ofthe nanoscale wire, within about 20 nm of the nanoscale wire, withinabout 15 nm of the nanoscale wire, or within about 10 nm of thenanoscale wire. The actual proximity can be determined by those ofordinary skill in the art. In some cases, the binding partner ispositioned less than about 5 nm from the nanoscale wire. In other cases,the binding partner is positioned within about 4 nm, within about 3 nm,within about 2 nm, or within about 1 nm of the nanoscale wire.

In some embodiments, the binding partner is fastened to or directlybonded (e.g., covalently) to the nanoscale wire, e.g., as furtherdescribed herein. However, in other embodiments, the binding partner isnot directly bonded to the nanoscale wire, but is otherwise immobilizedrelative to the nanoscale wire, i.e., the binding partner is indirectlyimmobilized relative to the nanoscale wire, as discussed above. Forinstance, the binding partner may be attached to the nanoscale wirethrough a linker, i.e., a species (or plurality of species) to which thebinding partner and the nanoscale wire are each immobilized relativethereto, e.g., covalently or non-covalently bound to. As an example, alinker may be directly bonded to the nanoscale wire, and the bindingpartner may be directly bonded to the linker, or the binding partner maynot be directly bonded to the linker, but immobilized relative to thelinker, e.g., through the use of non-covalent bonds such as hydrogenbonding (e.g., as in complementary nucleic acid-nucleic acidinteractions), hydrophobic interactions (e.g., between hydrocarbonchains), entropic interactions, or the like. The linker may or may notbe directly bonded (e.g., covalently) to the nanoscale wire.

Non-limiting examples of chemistries suitable for immobilizing bindingpartners relative to nanoscale wires, optionally via one or morelinkers, include the following. In one set of embodiments, the surfaceof the nanoscale wire may be functionalized. For example, the surfacemay be functionalized with aldehydes, amines, thiols, or the like, whichmay form nitrogen-containing or sulfur-containing covalent bonds. Insome embodiments, for instance, the binding partner may be covalentlybound to the nanoscale wire through the use of a moiety such as analdehyde moiety, an amine moiety, and/or a thiol moiety.

In certain embodiments, a nanoscale wire is reacted with an aldehyde,amine, and/or a thiol to functionalize the nanoscale wire with theappropriate moiety, e.g., such that the surface of the nanoscale wireincludes terminal aldehyde, amine, and/or thiol groups (for example, asa monolayer). In some embodiments, a solution may contain a silanecomprising an aldehyde moiety, for example, aldehydes such as aldehydepropyltrimethoxysilane ((CH₃O)₃SiCH₂CH₂CHO), or other aldehydes, forinstance, having a formula such as (OCHR¹)(R²O)(R³O)(R⁴O)Si,(OCHR¹)R²R³XSi, (OCHR¹)R²X¹X²Si, or (OCHR¹)X¹X²X³Si, where each R isindependently an alkyl or other carbon-containing moiety, a silanecomprising an amine moiety, a silane comprising a thiol moiety, etc.;and each X is independently a halogen. All, or only a portion of, thesurface of the nanoscale wire may be functionalized, for instance, withaldehyde moieties (for example, a portion of the nanoscale wire may beblocked or shielded, prior to aldehydization of the surface).

Additional non-limiting examples of suitable amines or thiols includeamino- and thiol-functionalized silane derivatives, for instance,trimethoxy propylamine silane ((CH₃O)₃SiCH₂CH₂CH₂NH₂) or propylthioltrimethoxy silane ((CH₃O)₃SiCH₂CH₂CH₂SH), which may react with all, oronly a portion of, the surface of the nanoscale wire to form, surfacesfunctionalized with, respectively, amines or thiols. Other potentiallysuitable amines may have a formula (Z¹Z²NR¹)(R²O)(R³O)(R⁴O)Si, whereeach R is independently an alkyl or other carbon-containing moiety andeach Z independently is —H or an alkyl or other carbon-containingmoiety; other potentially suitable thiols may have a formula(HSR¹)(R²O)(R³O)(R⁴O)Si. In some cases, the derivative may have morethan one functional group, for example, the derivative may have an amineand a thiol group, an amine and an aldehyde group, a thiol and analdehyde group, etc.

One or more binding partners, e.g., nucleic acids, proteins, enzymes,antibodies, receptors, ligands, etc., may be reacted with the aldehyde,amine, and/or thiol moieties to covalently bind the binding partner tothe nanoscale wire. For instance, a nucleic acid or other bindingpartner may be modified with an amine group or a maleimide group. Thebinding partner may then be immobilized with respect to the surface viareaction between the amine and an aldehyde or epoxy, between themaleimide group and a thiol, etc.

In some cases, after the binding partner has been fastened to thenanoscale wire, the surface of the nanoscale wire, including anyunreacted moieties, is then passivated, e.g., blocked with one or morecompounds that causes the moieties to become unreactive. Non-limitingexamples of such passivating agents include ethanolamine, e.g., to blockunreacted aldehyde groups. For example, a solution may be added to thenanowires that includes one or more passivating agents.

Additional non-limiting examples of chemistries suitable for attachingbinding partners to nanoscale wires are disclosed in U.S. ProvisionalPatent Application Ser. No. 60/707,136, filed Aug. 9, 2005, entitled“Nanoscale Sensors,” by Lieber, et al., incorporated herein byreference.

The invention, in some embodiments, involves a sensing element (whichcan be an electronic sensing element) comprising a sample exposureregion and a nanoscale wire able to detect the presence or absence of ananalyte, and/or the concentration of the analyte, in a sample (e.g. afluid sample) containing, or suspected of containing, the analyte,and/or to determine dynamic information, e.g., association and/ordissociation of the analyte with the binding partner (for instance,association rate, dissociation rate, binding constant, rate constant,etc.). The “sample exposure region” may be any region in close proximityto the nanoscale Wire where a sample in the sample exposure regionaddresses at least a portion of the nanoscale wire. Examples of sampleexposure regions include, but are not limited to, a well, a channel, amicrofluidic channel, or a gel. In certain embodiments, the sampleexposure region is able to hold a sample proximate the nanoscale wire,and/or may direct a sample toward the nanoscale wire for determinationof an analyte in the sample. The nanoscale wire may be positionedadjacent or within the sample exposure region. Alternatively, thenanoscale wire may be a probe that is inserted into a fluid or fluidflow path. The nanoscale wire probe may also comprise, in someinstances, a microneedle that supports and/or is integral with thenanoscale wire, and the sample exposure region may be addressable by themicroneedle. In this arrangement, a device that is constructed andarranged for insertion of a microneedle probe into a sample can includea region surrounding or otherwise in contact with the microneedle thatdefines the sample exposure region, and a sample in the sample exposureregion is addressable by the nanoscale wire, and vice versa. Fluid flowchannels can be created at a size and scale advantageous for use in theinvention (e.g., microchannels) using a variety of techniques such asthose described in International Patent Application Serial No.PCT/US97/04005, entitled “Method of Forming Articles and PatterningSurfaces via Capillary Micromolding,” filed Mar. 14, 1997, published asInternational Patent Application Publication No. WO 97/33737 on Sep. 18,1997, and incorporated herein by reference.

As a non-limiting example, a sample, such as a fluid suspected ofcontaining an analyte that is to be determined, may be presented to asample exposure region of a sensing element comprising a nanoscale wire.An analyte present in the fluid that is able to bind to the nanoscalewire and/or a binding partner immobilized relative to the nanoscale wiremay cause a change in a property of the nanoscale wire that isdeterminable upon binding, e.g. using conventional electronics. If theanalyte is not present in the fluid, the relevant property of thenanoscale wire will remain substantially unchanged, and the detectorwill measure no significant change. Thus, according to this particularexample, the presence or absence of an analyte can be determined bymonitoring changes, or lack thereof, in the property of the nanoscalewire. In some cases, if the detector measures a change, the magnitude ofthe change may be a function of the concentration of the analyte, and/ora function of some other relevant property of the analyte (e.g., chargeor size, etc.). Thus, by determining the change in the property of thenanoscale wire, the concentration or other property of the analyte inthe sample may be determined.

A “fluid,” as used herein, generally refers to a substance that tends toflow and to conform to the outline of its container. Typically, fluidsare materials that are unable to withstand a static shear stress. When ashear stress is applied to a fluid, it experiences a continuing andpermanent distortion. Typical fluids include liquids and gases, but mayalso include free-flowing solid particles, viscoelastic fluids, and thelike.

Where a detector is present, any detector capable of determining aproperty associated with a nanoscale wire can be used, which can be usedto determine the analyte. The property can be electronic, optical, orthe like. An electronic property of a nanoscale wire can be, forexample, its conductivity, resistivity, etc, as previously described.For example, the detector can be constructed for measuring a change inan electronic or magnetic property (e.g. voltage, current, conductivity,resistance, impedance, inductance, charge, etc.). The detector typicallyincludes a power source and a voltmeter and/or an ammeter. In oneembodiment, a conductance less than 1 nS can be detected. In some cases,a conductance in the range of thousandths of nS can be detected. Theconcentration of a species, or analyte, may be detected from less thanmicromolar to molar concentrations and above. By using nanoscale wireswith known detectors, sensitivity can be extended to a single molecule,and/or a single mismatch within a single nucleic acid molecule.

As another example, one or more different nanoscale wires may cross thesame microfluidic channel (e.g., at different positions) to detect thesame or different analytes, to measure a flowrate of an analyte(s), etc.In another embodiment, one or more nanoscale wires may be positioned ina microfluidic channel to form one of a plurality of analytic elements,for instance, in a microneedle probe, a dip and read probe, etc. Theanalytic elements probe may be implantable and capable of detectingseveral analytes simultaneously in real time, according to certainembodiments. In another embodiment, one or more nanoscale wires may bepositioned in a microfluidic channel to form an analytic element in amicroarray for a cassette or a lab-on-a-chip device. Those of ordinaryskill in the art would know of examples of cassette or lab-on-a-chipdevices that are suitable for high-throughout chemical analysis andscreening, combinational drug discovery, etc.

Another set of embodiments of the present invention provides an articlecomprising one or more nanoscale wires and a detector constructed andarranged to determine a change in an electrical property of thenanoscale wire. For example, at least a portion of the nanoscale wires(which may be aligned in some cases) is addressable by a samplecontaining, or suspected of containing, an analyte. The phrase“addressable by a fluid” is defined as the ability of the fluid to bepositioned relative to the nanoscale wire so that an analyte suspectedof being in the fluid is able to interact with the nanoscale wire. Thefluid may be proximate to or in contact with the nanoscale wire.

Additional examples of such systems, and techniques for using suchsystems (e.g., for detecting “false positive” events, for detectingmultiple analytes simultaneously and/or sequentially, for detecting datein real time and/or near-real time, for detecting analyte binding as afunction of time, for use of arrays and/or cassettes containing multiplenanoscale wires, for computer control and/or integrated devices, etc.),are disclosed in U.S. patent application Ser. No. 11/137,784, filed May25, 2005, entitled “Nanoscale Sensors,” by Lieber, et al.; U.S.Provisional Patent Application Ser. No. 60/790,322, filed Apr. 7, 2006,entitled “Nanoscale Wire Methods and Devices,” by Lieber, et al.; orU.S. Provisional Patent Application Ser. No. 60/707,136, filed Aug. 9,2005, entitled “Nanoscale Sensors,” by Lieber, et al., each incorporatedherein by reference.

Certain aspects of the invention are directed to techniques forfabricating nanoscale wires, e.g., containing portions to which bindingpartners or other reaction entities may be immobilized relative thereto.The criteria for selection of nanoscale wires and other conductors orsemiconductors for use in the invention are based, in some instances,upon whether the nanoscale wire itself is able to interact with ananalyte, whether the appropriate binding partner can be easily attachedto the surface of the nanoscale wire, and/or whether the appropriatebinding partner is near the surface of the nanoscale wire. Selection ofsuitable conductors or semiconductors, including nanoscale wires, willbe apparent and readily reproducible by those of ordinary skill in theart with the benefit of the present disclosure.

In one aspect, the present invention provides a method of preparing ananostructure. In one set of embodiments, the method involves allowing afirst material to diffuse into at least part of a second material,optionally creating a new compound. For example, the first and secondmaterials may each be metals or semiconductors, one material may be ametal and the other material may be a semiconductor (e.g., creating ametal-semiconductor compound), etc. In one set of embodiments, asemiconductor may be annealed to a metal. For example, a portion of thesemiconductor and/or a portion of the metal may be heated such that atleast some metal atoms are able to diffuse into the semiconductor, orvice versa. In one embodiment, a metal electrode (e.g., a nickel, gold,copper, silver, chromium electrode, etc.), may be positioned in physicalcontact with a semiconductor nanoscopic wire, and then annealed suchthat at least a portion of the semiconductor diffuses into at least aportion of the metal, optionally forming a metal-semiconductor compound,e.g., as disclosed in International Patent Application No.PCT/US2005/004459, filed Feb. 14, 2005, entitled “NanostructuresContaining Metal-Semiconductor Compounds,” published as WO 2005/093831on Oct. 6, 2005 by Lieber, et al., or U.S. Provisional PatentApplication Ser. No. 60/707,136, filed Aug. 9, 2005, entitled “NanoscaleSensors,” by Lieber, et al., each incorporated herein by reference. Forexample, the semiconductor may be annealed with the metal at atemperature of about 300° C., about 350° C., about 400° C., about 450°C., about 500° C., about 550° C., about 600° C., etc., for a period oftime of at least about 30 minutes, at least about 1 hour, at least about2 hours, at least about 4 hours, at least about 6 hours, etc. Suchannealing may allow, for example, lower contact resistances orimpedances between the metal and the semiconductor.

As used herein, a “metal-semiconductor compound” is a compound thatincludes at least one metal combined with a semiconductor. Inmetal-semiconductor compounds of the invention, at least one portion ofthe compound includes a metal and a semiconductor present in astoichiometrically defined ratio, i.e., the metal atoms and thesemiconductor atoms are present within the compound (i.e., on the atomicscale) in a whole number ratio that is chemically defined, i.e., definedon the basis of the atomic interactions between the metal atoms and thesemiconductor atoms within the compound that lead to a ratio of elementspresent dictated by the bonding principles of chemistry (e.g.coordination chemistry, atomic and molecular orbital interactions andformation, crystal packing, and/or the like). This is to bedistinguished from alloys or mixtures, which are simply blends of two ormore atoms in a substance, in which the atoms can be mixed together inany ratio, where the ratio is not determined by stoichiometricinteractions between the atoms, and doping, where, e.g., ion bombardmentof a material with a dopant leads to non-stoichiometric amounts of thedopant in the host material dictated by the amount of dopant introduced.Instead, the metal atoms and the semiconductor atoms in ametal-semiconductor compound interact on the atomic level in a definedfashion, thus resulting in the metal-semiconductor compound having awhole number ratio between the metal atoms and the semiconductor atomswithin the compound, i.e., the ratio is dictated by atomic interactionsbetween the metal atoms and the semiconductor atoms within the compound.Thus, the stoichiometric ratio between the metal atoms and thesemiconductor atoms is always the same on the atomic level (i.e., at anylocation within the compound). As an example, there may be ionic chargedinteractions between the metal atoms and the semiconductor atoms suchthat, for charge neutrality, there is a stoichiometric ratio between themetal atoms and the semiconductor atoms within the compound, forexample, MZ, M₂Z, M₂Z₃, MZ₂, M₃Z₂, or the like, where M is a metal and Zis a semiconductor. A specific non-limiting example is nickel silicide,NiSi. In some cases, more than one type of metal atom and/or more thanone type of semiconductor atom may be present in the metal-semiconductorcompound. It should be recognized, of course, that measurements of theratio of two or more atoms in a compound are not necessarily alwaysexact, due to experimental error and other practical limitations. Thus,in some cases, the ratio so measured may be stoichiometric in reality,even though the experimental measurements deviate somewhat from wholenumber ratios. As an example, the actual ratios determined for ametal-semiconductor compound may be within about 10% or about 5% of astoichiometric, whole number ratio.

In one set of embodiments, the metal within the metal-semiconductorcompound is a transition metal, for example, an element from one or moreof Group IB, Group IIB, Group IIIB, Group IVB, Group VB, Group VIB,Group VIIB, or Group VIIIB. In some cases, Group VIIIB metals may beparticularly useful within the metal-semiconductor compound, forexample, nickel, iron, palladium, platinum, iridium, etc.

In one embodiment, a first material is positioned adjacent or proximateto a second material (by known forms of deposition, for example), andthe atoms of the first material are allowed to diffuse into at least aportion of the second material. At least one of the first and secondmaterials may be a nanoscale material. Thus, as an example, in FIG. 1A,a first material 51 is positioned next to a second material 52. Thefirst material may be positioned such that it contacts the secondmaterial, and/or such that atoms from the first material are able todiffuse into the second material (for example, an intervening materialor space may be present between the first material and the secondmaterial). Diffusion of the first material into at least a portion ofthe second material is then allowed to occur, as shown in FIG. 1B. Whensufficient diffusion has occurred (i.e., when a desired amount of thefirst material has diffused into the second material), the firstmaterial (or at least a portion thereof) may optionally be removed, asis shown in FIG. 1C. In a nanoscale wire, the diffusion may be axialand/or longitudinal along the nanoscale wire, and in some cases, thediffusion rate (e.g., in either or both directions) may be controlled bycontrolling the size or diameter of the nanoscale wires. For instance,in some cases, thinner nanoscale wires may result in higher diffusionrates.

As an example, to create a nanoscale wire comprising ametal-semiconductor compound, a metal may be positioned adjacent orproximate to a semiconductor (by known forms of deposition, forexample), and the metal atoms allowed to diffuse into at least a portionof the semiconductor material, for example, to create one or moreheterojunctions within the nanoscale wire. The metal may be a bulk metalin some cases, i.e., a metal having a volume of at least nanoscopicdimensions (e.g., having a smallest dimension of at least about 1 nm).

In some cases, diffusion of the metal atoms into the semiconductor maybe initiated and/or facilitated, for example, by the application of highpressures and/or high temperatures, for example, temperatures of atleast about 500° C., at least about 550° C., at least about 600° C., atleast about 700° C., or more in some cases. The diffusion rate may becontrolled by the annealing temperature and/or the time of annealing,and the amount and/or length of diffusion can be readily optimized for aparticular application using routine experimentation. In certaininstances, substantial diffusion of metal atoms into the semiconductormay not substantially occur absent an increase or an alteration in thetemperature and/or pressure. In some cases, diffusion of the metal atomsinto the semiconductor (or at least a portion thereof) may proceed untila metal-semiconductor compound forms (e.g., through a chemicalreaction), and/or when a stoichiometric ratio of metal atoms tosemiconductor atoms has been established. As a particular example, ifthe metal is a transition metal such as nickel, and the semiconductormaterial is a silicon nanoscale wire, diffusion of nickel into thesilicon nanoscale wire may proceed until the silicon nanoscale wire (orat least that portion of the nanoscale wire exposed to nickel) has beenconverted into nickel silicide. In other cases, however, the metal atomsand the semiconductor atoms may not be in a stoichiometric ratio. Incertain instances, diffusion of the metal into the semiconductor may bestopped before metal-semiconductor compound formation or stoichiometricequilibrium has been established; thus, in one embodiment, the nanoscalewire may include a non-stoichiometric ratio of metal atoms tosemiconductor atoms. The diffusion of the metal into the semiconductormay be determined using techniques known to those of ordinary skill inthe art, such as SEM, TEM, AFM, EFM, etc.

After the metal atoms have been allowed to diffuse into thesemiconductor, in some cases, excess metal may be removed from thesemiconductor, for example, by the application of certain species suchas metal etchants. For example, if the metal diffused into thesemiconductor is nickel, a suitable metal etchant may include acids suchas nitric acid, sulfuric acid, hydrochloric acid, and/or nickel etchantssuch as TFB or TFG (available from Transene, Danvers, Mass.). In somecases, the removal of the excess metal from the semiconductor may befacilitated by elevated temperatures and/or pressures.

Thus, in one embodiment, a nanoscale wire may be prepared having a firstportion, defined by diffusion of a metal into the nanoscale wire, and asecond portion that the metal did not diffuse into. For example, asillustrated in FIG. 1D, a semiconductor 10 having first and secondportions may be prepared by exposing a portion of the nanoscale wire toa metal 15, and allowing the metal ions to diffuse into thesemiconductor to create a first portion 11 and a second portion 12. Thefirst portion 11 may be defined by the diffusion of the metal into thesemiconductor, while the second portion 12 may be defined by portions ofthe semiconductor free of the metal, and such portions may be radiallyand/or longitudinally positioned along the nanoscale wire.

The size of the portions may be controlled, for instance, by controllingthe temperature of the semiconductor and/or the annealing time. Forinstance, by heating the nanoscale wire to diffuse the metal into thesemiconductor, then cooling the nanoscale wire once the metal hasdiffused a predetermined distance into the semiconductor, the size ofthe second portion may be controlled as desired. For example, referringto FIG. 1D, the size of first portion 11 of the semiconductor may be nogreater than about 900 nm, than about 750 nm, than about 500 nm, thanabout 300 nm, than about 100 nm, than about 50 nm, than about 30 nm,than about 10 nm, etc., away from metal 15; and/or the size of secondportion 12 of the semiconductor may be no greater than about 900 nm,than about 750 nm, than about 500 nm, than about 300 nm, than about 100nm, than about 50 nm, than about 30 nm, than about 10 nm, etc. In somecases, first and/or second portions may be measured relative to theoverall length of semiconductor 10, e.g., measured from metal 15. Forinstance, diffusion of the metal may occur within semiconductor 10 suchthat less than about 10%, less than about 20%, less than about 30%, lessthan about 40%, less than about 50%, less than about 60%, less thanabout 70%, less than about 80%, less than about 90%, etc. of thesemiconductor comprises the first region.

As previously mentioned, the diffusion of the metal atoms into thesemiconductor may be facilitated, for example, by the application ofhigh pressures and/or high temperatures, for example, temperatures of atleast about 500° C., at least about 550° C., at least about 600° C., atleast about 700° C., or more in some cases. In certain instances,substantial diffusion of metal atoms into the semiconductor may notsubstantially occur absent an increase or an alteration in thetemperature and/or pressure.

In another set of embodiments, a nanostructure can be prepared byexposing a portion of the second material to the first material. Thefirst material can diffuse into regions of the second material that areadjacent or proximate the first material, while regions of the secondmaterial not adjacent or proximate the first material will remainsubstantially free of the first material. As one example, as shown inFIG. 1E, a mask 38 may be patterned on a nanostructure 37 (or othernanostructure) to define one or more regions where the nanostructure iscovered by the mask 60 and one or more regions where the nanostructureis free of the mask 65. The mask may have any pattern defined therein,and can define 2- or 3-dimensional patterns on the nanostructure,depending on the specific application. Any suitable material may be usedto form the mask, for instance, a photoresist may be formed on thenanostructure to define a mask, e.g., through photolithographictechniques known to those of ordinary skill in the art. As anon-limiting example, a mask with a series of openings may be formed ona nanowire to create a series of heterojunctions along the nanowire, orif not formed on the nanowire (or other nanostructure), positioned inproximity relative to the nanowire so as to be able to mask applicationof material on the nanowire. As another example, a mask may be formedfrom a nanoscale wire, for example, a nanoscale wire, a nanotube, acore/shell nanoscale wire, etc. For instance, the nanoscale wire used asa mask may be placed on or positioned in proximity to the nanowire (orother nanostructure); the nanoscale wire used as a mask may thus maskapplication of material on the nanowire.

After positioning of the mask on the second material of thenanostructure, or between the nanostructure and the source of materialto be deposited thereto, the first material may be deposited on themask. Regions of the nanostructure that are free of the mask 65 willhave the first material deposited thereon, while regions of thenanostructure covered by the mask 60 will not be exposed to the firstmaterial. The first material can then diffuse into the portions secondmaterial adjacent or proximate the first material. The mask may beremoved before or after diffusion of the first material into portions ofthe second material. After diffusion, a nanostructure having one or moreheterojunctions 67, defined by the mask, can be created.

In one set of embodiments, a reaction entity or a binding partner may beimmobilized relative to all of the nanoscale wire, or to only a portionof the nanoscale wire, for example, immobilized relative to a secondportion of the nanoscale wire. In some cases, more than one type ofreaction entity and/or binding partner may immobilized to a secondportion of a nanoscale wire, and/or to different portions of thenanoscale wire.

Thus, in some cases, a nanoscale wire may be prepared having a firstportion comprising a metal-semiconductor compound, and a second portionthat does not include a metal-semiconductor compound. Immobilizedrelative to the second portion (or “channel”) of the nanoscale wire maybe one or more binding partners, e.g., directly attached or indirectlyattached, for instance, via a linker, as described above. Minimizing thesize of the second portion of the nanoscale wire, relative to the firstportion of the nanoscale wire, in some cases, may facilitatedetermination of an analyte (for example, its kinetics or otherdynamical information), such as a nucleic acid, for instance, due to thesmall area of the second portion and the relatively few numbers ofbinding partners that are immobilized relative thereto. In some cases,binding events to other portions of a nanoscale wire (e.g., otherportions of a nanoscale wire having binding partners) may not affectchanges (or may affect to a lesser or insubstantial degree) inelectrical properties of those other portions (as an example, in ananoscale wire having metal-semiconductor compounds, those portions ofthe metal-semiconductor compound may be metallic, and binding of ananalyte to binding partners immobilized relative to those portions ofthe nanoscale wire may not significantly alter the electrical propertiesof the nanoscale wire). Also, by minimizing the sizes of the contacts tothe second portion of the nanoscale wire and/or the electrostatic fieldeffect from them, the signal due to binding of the analyte to thenanoscale wire may be enhanced. Thus, for instance, due to the smallnumber of binding partners bound to the second portion of the nanoscalewire and/or enhanced signal from the analyte, the binding of even asingle molecule (or a small number of molecules) of analyte to one ofthe binding partners may be detected, e.g., as a change in an electricalproperty (e.g., resistance or conductivity) of the nanoscale wire. Seealso Example 5 for an illustration of this sensitivity. Thus, in somecases, single binding events of an analyte, such as a nucleic acid, to ananoscale wire may be determined, and in some cases, the identity ofsimilar analytes may be determined, e.g., through differences in bindingcharacteristics, e.g., through determination of binding constants, ratesof association and/or dissociation, etc.

In addition, in some cases, such as with nucleic acids such as DNA, acharged analyte bound to a binding partner immobilized relative to ananowire may “expel” or prevent other charged analytes from binding tonearby binding partners. This “charge separation” effect may bedetermined, for instance, by determining the “Debye screening length.”As known to those of ordinary skill in the art, the Debye screeninglength can vary for a particular analyte in a particular solution, e.g.,due to the presence of other ions in solution. As an example, for DNA,the Debye screening length in a typical buffer solution may be between30 nm and 100 nm. Due to the screening effect, only a small number ofanalytes can bind to a nanoscale wire, and in certain cases, e.g., ifthe portion of the nanoscale wire having binding partners issufficiently small, e.g., of the same order of magnitude as the Debyescreening length, or even smaller, then only a single analyte molecule(e.g., one nucleic acid molecule) may be able to become immobilizedrelative to the nanoscale wire. Thus, in one embodiment, a solution maycomprise an analyte and a nanoscale wire comprising a portion havingimmobilized relative thereto a binding partner to the analyte, where theDebye screening length of the analyte is greater than the greatestdimension of the portion of the nanoscale wire having the bindingpartner.

Some aspects of the invention may utilize various techniques tofabricate or synthesize individual nanoscale wires. For example, in someembodiments, metal-catalyzed CVD techniques (“chemical vapordeposition”) may be used to synthesize individual nanoscale wires. CVDsynthetic procedures useful for preparing individual wires directly onsurfaces and in bulk form are generally known, and can readily becarried out by those of ordinary skill in the art.

One technique that may be used to grow nanoscale wires is catalyticchemical vapor deposition (“C-CVD”). In the C-CVD method, the reactantmolecules are formed from the vapor phase, as opposed to from laservaporization. In C-CVD, nanoscale wires may be doped by introducing thedoping element into the vapor phase reactant (e. g. diborane andphosphane for p-type and n-type doped regions). The doping concentrationmay be controlled by controlling the relative amount of the dopingcompound introduced in the composite target.

Nanoscopic wires may also be grown through laser catalytic growth. See,for example, Morales, et al., “A Laser Ablation Method for the Synthesisof Crystalline Semiconductor Nanowires,” Science, 279:208-211 (1998). Inlaser catalytic growth, dopants may be controllably introduced duringvapor phase growth of nanoscale wires. Laser vaporization of a compositetarget composed of a desired material (e. g. silicon or indiumphosphide) and a catalytic material (e. g. a nanoparticle catalyst) cancreate a hot, dense vapor. The vapor condenses into liquid nanoclustersthrough collision with a buffer gas. Growth may begin when the liquidnanoclusters become supersaturated with the desired phase and cancontinue as long as reactant is available. Growth may terminate when thenanoscale wire passes out of the hot reaction zone or when thetemperature is decreased. The nanoscale wire may be further subjected todifferent semiconductor reagents during growth. If uniform diameternanoclusters (e.g., less than 10-20% variation depending on how uniformthe nanoclusters are) are used as the catalytic cluster, nanoscale wireswith uniform size (diameter) distribution can be produced, where thediameter of the nanoscale wires is determined by the size of thecatalytic clusters.

Other techniques to produce nanoscale semiconductors such as nanoscalewires are also within the scope of the present invention. For example,nanoscale wires of any of a variety of materials may be grown directlyfrom vapor phase through a vapor-solid process. Also, nanoscale wiresmay also be produced by deposition on the edge of surface steps, orother types of patterned surfaces. Further, nanoscale wires may be grownby vapor deposition in or on any generally elongated template. Theporous membrane may be porous silicon, anodic alumina, a diblockcopolymer, or any other similar structure. The natural fiber may be DNAmolecules, protein molecules carbon nanotubes, or any other elongatedstructures. For the above described techniques, the source materials maybe a solution or a vapor.

In some cases, the nanoscale wire may be doped after formation. In onetechnique of post-synthetic doping of nanoscale wires, a nanoscale wirehaving a substantially homogeneous composition is first synthesized,then is doped post-synthetically with various dopants. Such doping mayoccur throughout the entire nanoscale wire, or in one or more portionsof the nanoscale wire, for example, in a wire having multiple regionsdiffering in composition. Thus, as a specific non-limiting example, asemiconductor nanoscale wire may be prepared, then one or more regionsof the nanoscale wire may be exposed to a dopant, thus resulting in asemiconductor nanoscale wire having a series of undoped semiconductorregions and doped semiconductor regions.

In one set of embodiments, the invention includes a nanoscale wire (orother nanostructured material) that is a single crystal. As used herein,a “single crystal” item (e.g., a semiconductor) is an item that hascovalent bonding, ionic bonding, or a combination thereof throughout theitem. Such a single-crystal item may include defects in the crystal, butis to be distinguished from an item that includes one or more crystals,not ionically or covalently bonded, but merely in close proximity to oneanother.

Various embodiments of the invention include the assembly, or controlledplacement, of nanoscale wires on a surface. Any substrate may be usedfor nanoscale wire placement, for example, a substrate comprising asemiconductor, a substrate comprising a metal, a substrate comprising aglass, a substrate comprising a polymer, a substrate comprising a gel, asubstrate that is a thin film, a substantially transparent substrate, anon-planar substrate, a flexible substrate, a curved substrate, etc. Insome cases, assembly can be carried out by aligning nanoscale wiresusing an electrical field. In other cases, assembly can be performedusing an arrangement involving positioning a fluid flow directingapparatus to direct fluid containing suspended nanoscale wires towardand in the direction of alignment with locations at which nanoscalewires are desirably positioned.

In certain cases, a nanoscale wire (or other nanostructure) is formed onthe surface of a substrate, and/or is defined by a feature on asubstrate. In one example, a nanostructure, such as a nanoscale wire, isformed as follows. A substrate is imprinted using a stamp or otherapplicator to define a pattern, such as a nanoscale wire or othernanoscale structure. After removal of the stamp or other applicator, atleast a portion of the imprintable layer is removed, for example,through etching processes such as reactive ion etching (RIE), or otherknown techniques. In some cases, enough imprintable material may beremoved from the substrate so as to expose portions of the substratefree of the imprintable material. A metal or other materials may then bedeposited onto at least a portion of the substrate, for example, gold,copper, silver, chromium, etc. In some cases, a “lift-off” step may thenbe performed, where at least a portion of the imprintable material isremoved from the substrate. Metal or other material deposited onto theimprintable material may be removed along with the removal of theimprintable material, for example, to form one or more nanoscale wires.Structures deposited on the surface may be connected to one or moreelectrodes in some cases. The substrate may be any suitable substratethat can support an imprintable layer, for example, comprising asemiconductor, a metal, a glass, a polymer, a gel, etc. In some cases,the substrate may be a thin film, substantially transparent, non-planar,flexible, and/or curved, etc.

In certain cases, an array of nanoscale wires may be produced byproviding a surface having a plurality of substantially alignednanoscale wires, and removing, from the surface, a portion of one ormore of the plurality of nanoscale wires. The remaining nanoscale wireson the surface may then be connected to one or more electrodes. Incertain cases, the nanoscopic wires are arranged such that they are incontact with each other; in other instances, however, the alignednanoscopic wires may be at a pitch such that they are substantially notin physical contact.

In certain cases, nanoscale wires are positioned proximate a surfaceusing flow techniques, i.e., techniques where one or more nanoscalewires may be carried by a fluid to a substrate. Nanoscale wires (or anyother elongated structures) can be aligned by inducing a flow of ananoscale wire solution on surface, where the flow can include channelflow or flow by any other suitable technique. Nanoscale wire arrays withcontrolled position and periodicity can be produced by patterning asurface of a substrate and/or conditioning the surface of the nanoscalewires with different functionalities, where the position and periodicitycontrol may be achieved by designing specific complementary forcesbetween the patterned surface and the nanoscale wires. Nanoscale wirescan also be assembled using a Langmuir-Blodgett (LB) trough. Nanoscalewires may first be surface-conditioned and dispersed to the surface of aliquid phase to form a Langmuir-Blodgett film. In some cases, the liquidmay include a surfactant, which can, in some cases, reduce aggregationof the nanoscale wires and/or reduce the ability of the nanoscale wiresto interact with each other. The nanoscale wires can be aligned intodifferent patterns (such as parallel arrays or fibers) by compressingthe surface or reducing the surface area of the surface.

Another arrangement involves forming surfaces on a substrate includingregions that selectively attract nanoscale wires surrounded by regionsthat do not selectively attract them. Surfaces can be patterned usingknown techniques such as electron-beam patterning, “soft-lithography”such as that described in International Patent Application Serial No.PCT/US96/03073, entitled “Microcontact Printing on Surfaces andDerivative Articles,” filed Mar. 1, 1996, published as Publication No.WO 96/29629 on Jul. 26, 1996; or U.S. Pat. No. 5,512,131, entitled“Formation of Microstamped Patterns on Surfaces and DerivativeArticles,” issued Apr. 30, 1996, each of which is incorporated herein byreference. Additional techniques are described in U.S. PatentApplication Ser. No. 60/142,216, entitled “Molecular Wire-Based Devicesand Methods of Their Manufacture,” filed Jul. 2, 1999, incorporatedherein by reference. Fluid flow channels can be created at a size scaleadvantageous for placement of nanoscale wires on surfaces using avariety of techniques such as those described in International PatentApplication Serial No. PCT/US97/04005, entitled “Method of FormingArticles and Patterning Surfaces via Capillary Micromolding,” filed Mar.14, 1997, published as Publication No. WO 97/33737 on Sep. 18, 1997, andincorporated herein by reference. Other techniques include thosedescribed in U.S. Pat. No. 6,645,432, entitled “Microfluidic SystemsIncluding Three-dimensionally Arrayed Channel Networks,” issued Nov. 11,2003, incorporated herein by reference.

Chemically patterned surfaces other than SAM-derivatized surfaces can beused, and many techniques for chemically patterning surfaces are known.Another example of a chemically patterned surface may be a micro-phaseseparated block copolymer structure. These structures may provide astack of dense lamellar phases, where a cut through these phases revealsa series of “lanes” wherein each lane represents a single layer. Theassembly of nanoscale wires onto substrate and electrodes can also beassisted using bimolecular recognition in some cases. For example, onebiological binding partner may be immobilized onto the nanoscale wiresurface and the other one onto a substrate or an electrode usingphysical adsorption or covalently linking. An example technique whichmay be used to direct the assembly of a nanoscopic wires on a substrateis by using “SAMs,” or self-assembled monolayers. Any of a variety ofsubstrates and SAM-forming material can be used along with microcontactprinting techniques, such as those described in International PatentApplication Serial No. PCT/US96/03073, entitled “Microcontact Printingon Surfaces and Derivative Articles,” filed Mar. 1, 1996, published asPublication No. WO 96/29629 on Jul. 26, 1996, incorporated herein byreference in its entirety.

In some cases, the nanoscale wire arrays may also be transferred toanother substrate, e.g., by using stamping techniques. In certaininstances, nanoscale wires may be assembled using complementaryinteraction, i.e., where one or more complementary chemical, biological,electrostatic, magnetic or optical interactions are used to position oneor more nanoscale wires on a substrate. In certain cases, physicalpatterns may be used to position nanoscale wires proximate a surface.For example, nanoscale wires may be positioned on a substrate usingphysical patterns, for instance, aligning the nanoscale wires usingcorner of the surface steps or along trenches on the substrate.

In another set of embodiments, the nanoscale wires may be transferred toa substrate by contacting at least some of the nanoscale wires with thesecond substrate, e.g., by moving or “sliding” the substrates relativeto each other, in some cases causing alignment of the nanoscale wires onthe second substrate. For instance, in one embodiment, a firstsubstrate, having a plurality of nanoscale wires thereon, is broughtinto contact with a second substrate to transfer one or more nanoscalewires from one to the other. The first substrate can then be moved orslid against a second substrate (and/or the second substrate is movedagainst the first substrate) such that at least some of the nanoscalewires are transferred from the first substrate to the second substrate.The nanoscale wires can become immobilized relative to the secondsubstrate through ionic interactions, hydrophobic interactions, van derWaals interactions, etc., or the like. Further details, as well asadditional methods of nanoscale wire transfer useful in the presentinvention, are discussed in U.S. Provisional Patent Application Ser. No.60/790,322, filed Apr. 7, 2006, entitled “Nanoscale Wire Methods andDevices,” by Lieber, et al., incorporated herein by reference.

The present invention finds use in a wide range of applications. Forinstance, in some aspects, any of the techniques described herein may beused in the determination of viruses, cells, or the like, e.g., as in anassay, for example, to detect or diagnose cancer or other medicalconditions, toxins or other environmental agents, viruses, or the like.As a specific, non-limiting example, specific DNA or RNA may beidentified from a virus under study, while the number of mismatches witha known binding Partner may be indicative of the viral strain of thevirus. As another example, mutations within a nucleic acid (e.g., withinDNA or RNA) may be determined using various systems and methods of theinvention, as previously described, for instance, if the sequence of thebinding partner to the nucleic acid is known, the degree of mutation maybe indicated by the number of mismatches present. The nucleic acidsample may be taken, for example, from a subject such as a human. In yetanother example, a property of an analyte may be determined by allowingthe analyte to interact with a binding partner, and the interaction maybe analyzed or determined in some fashion, e.g., quantified. In somecases, the degree or amount of interaction (e.g., a binding constant)may be determined, for example, by measuring a property of the nanoscalewire (e.g., an electronic property, such as the conductance) afterexposing the nanoscale wire and/or the binding partner to the analyte.

Another set of embodiments is generally directed to an array, such as amicroarray, of sensing regions. In some cases, at least some of thesensing regions each comprise one, or a plurality of, nanoscale wiresthat are individually addressable. In certain instances, at least someof the nanoscale wires comprise binding partners and/or reactionentities, such as those previously described. For example, in oneembodiment, some or all of the nanoscale wires may have differentbinding partners immobilized relative thereto, and optionally, eachnanoscale wire may be independently addressable and/or determinable,such that a plurality of different analytes may be detected, forexample, a plurality of different nucleic acids (which can be, in somecases, nucleic acids that are similar except for a small number ofmismatches as previously described, e.g., SNPs). Thus, the array may beused, for instance, to categorize an individual as a particular genetictype.

As a non-limiting example, DNA from a subject sample may be exposed toan array of nanoscale wires having binding partners to nucleic acidregions where SNPs often occur (e.g., nucleic acids that arecomplementary to those regions), and the presence of SNP alleles in theDNA may be determined, i.e., whether certain portions of the DNA bind tobinding partners on the array of nanoscale wires, and/or with whatdegree of binding. For instance, DNA from a first subject having a firstSNP allele such as a “wild-type” SNP allele may be perfectlycomplementary to a nucleic acid binding partner immobilized relative toa nanoscale wire on the array, while DNA from a second subject mayexhibit one or more mismatches to the nucleic acid binding partner,which mismatches can be detected, e.g., as described herein.

In some embodiments, the invention includes a microarray including aplurality of sensing regions, at least some of which comprise one ormore nanoscale wires. The microarray, including some or all of thesensing regions, may define a sensing element in a sensor device. Atleast some of the nanoscale wires are able to determine an analytesuspected to be present in a sample that the sensing region of themicroarray is exposed to, for example, the nanoscale wire may comprise areaction entity able to interact with an analyte. If more than onenanoscale wire is present within the sensing region, the nanoscale wiresmay be able to detect the same analyte and/or different analytes,depending on the application. For example, the nanoscale wires withinthe sensing region of the microarray may be able to determine 1, 2, 3,4, 5, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 40, 50, or moreanalytes or types of analytes. As an example, a microarray may have oneor more sensing regions, at least some of which comprise nanoscale wireshaving nucleic acids immobilized with respect to the nanoscale wires,e.g., as described herein. The microarray may be used to determineanalytes in one, or a number of samples. For example, the microarray mayinclude at least 2, at least 3, at least 5, at least 10, at least 15, atleast 20, at least 25, at least 30, at least 50, at least 70, at least100, at least 200, at least 300, at least 500, at least 1,000, at least3,000, at least 5,000, or at least 10,000 or more sensing regions, atleast some of which may be used to determine the analyte of a sampleplaced on the sensing region. In certain cases, the microarray may havea high density of nanoscale wires, at least some of which may be toindividually addressable, and at least some of which can be used todetermine an analyte suspected to be present in a sample. For instance,the density of nanoscale wires may be at least about 100 nanoscalewires/cm², and in some cases, at least about 110 nanoscale wires/cm², atleast about 120 nanoscale wires/cm², at least about 130 nanoscalewires/cm², at least about 150 nanoscale wires/cm², at least about 200nanoscale wires/cm², at least about 250 nanoscale wires/cm², or at leastabout 500 nanoscale wires/cm².

An example of a sensing region is shown in FIG. 6A. In this figure, thesensing region 220 includes a first electrode 221 and a second orcounter electrode 222. The first electrode is generally elongated (i.e.,one dimension of the electrode is significantly longer in one dimensionthan another). One or more nanoscale wires 227 are in electricalcommunication with first electrode 221 and second electrode 222, and atleast some of the nanoscale wires may comprise a reaction entity able tointeract with an analyte. First electrode 221 is in electroniccommunication with an electrical contact or lead 225 through electronicconnection 223 (e.g., a wire or an etched electronic pathway), whilesecond electrode 222 is in electronic communication with an electricalcontact 225 through electronic connection 224. Analyte 229 is present ina sample that is placed within sensing region 220, and is able tointeract with a reaction entity present on a nanoscale wire 227 (e.g.,by binding, for example, covalently). Upon such an interaction, anelectrical property of the nanoscale wire, e.g., conductivity, isaltered (e.g., through a charge interaction between the analyte and thenanoscale wire), which can be determined by determining a change inconductivity of the nanoscale wire, for instance, by measuring a changein conductivity between electrical contact 225 and electrical contact226.

Additional nanoscale wires may be added to the sensing region. Forexample, in FIG. 6B, sensing region 220 has five second or counterelectrodes 222. At least some of nanoscale wires 211, 212, 213, 214connect at least some of the second electrodes 222 with first electrode221, and at least some of the nanoscale wires may comprise a reactionentity able to interact with an analyte. For instance, nanoscale wires211 may interact with a first analyte, but not with a second analyte ora third analyte, while nanoscale wires 212 may interact with only thesecond analyte and nanoscale wires 213 may interact with only the thirdanalyte. Upon a binding event of an analyte with a correspondingreaction entity, a property of the nanoscale wire, such as conductance,may change, and may be determined, as previously described.

Additional arrays and microarrays useful in various embodiments of theinvention are discussed in U.S. Provisional Patent Application Ser. No.60/707,136, filed Aug. 9, 2005, entitled “Nanoscale Sensors,” by Lieber,et al., incorporated herein by reference.

In one aspect, the present invention provides any of the above-mentioneddevices packaged in kits, optionally including instructions for use ofthe devices. As used herein, “instructions” can define a component ofinstructional utility (e.g., directions, guides, warnings, labels,notes, FAQs (“frequently asked questions”), etc., and typically involvewritten instructions on or associated with packaging of the invention.Instructions can also include instructional communications in any form(e.g., oral, electronic, digital, optical, visual, etc.), provided inany manner such that a user will clearly recognize that the instructionsare to be associated with the device, e.g., as discussed herein.Additionally, the kit may include other components depending on thespecific application, for example, containers, adapters, syringes,needles, replacement parts, etc.

In some embodiments, one or more of the nanoscale wires describedherein, and/or one or more of the devices or methods described herein,may be promoted. As used herein, “promoted” includes all methods ofdoing business including, but not limited to, methods of selling,advertising, assigning, licensing, contracting, instructing, educating,researching, importing, exporting, negotiating, financing, loaning,trading, vending, reselling, distributing, replacing, or the like thatcan be associated with the methods and compositions of the invention,e.g., as discussed herein. Promoting may also include, in some cases,seeking approval from a government agency to sell a composition of theinvention for medicinal purposes. Methods of promotion can be performedby any party including, but not limited to, businesses (public orprivate), contractual or sub-contractual agencies, educationalinstitutions such as colleges and universities, research institutions,hospitals or other clinical institutions, governmental agencies, etc.Promotional activities may include instructions or communications of anyform (e.g., written, oral, and/or electronic communications, such as,but not limited to, e-mail, telephonic, facsimile, Internet, Web-based,etc.) that are clearly associated with the invention.

The following definitions will aid in the understanding of theinvention. Interspersed with these definitions is additional disclosureof various aspects of the invention.

Certain devices of the invention may include wires or other componentsof scale commensurate with nanometer-scale wires, which includesnanotubes and nanowires. In some embodiments, however, the inventioncomprises articles that may be greater than nanometer size (e. g.,micrometer-sized). As used herein, “nanoscopic-scale,” “nanoscopic,”“nanometer-scale,” “nanoscale,” the “nano-” prefix (for example, as in“nanostructured”), and the like generally refers to elements or articleshaving widths or diameters of less than about 1 micron, and less thanabout 100 nm in some cases. In all embodiments, specified widths can bea smallest width (i.e. a width as specified where, at that location, thearticle can have a larger width in a different dimension), or a largestwidth (i.e. where, at that location, the article has a width that is nowider than as specified, but can have a length that is greater).

As used herein, an “elongated” article (e.g. a semiconductor or asection thereof) is an article for which, at any point along thelongitudinal axis of the article, the ratio of the length of the articleto the largest width at that point is greater than 2:1.

A “width” of an article, as used herein, is the distance of a straightline from a point on a perimeter of the article, through the center ofthe article, to another point on the perimeter of the article. As usedherein, a “width” or a “cross-sectional dimension” at a point along alongitudinal axis of an article is the distance along a straight linethat passes through the center of a cross-section of the article at thatpoint and connects two points on the perimeter of the cross-section. The“cross-section” at a point along the longitudinal axis of an article isa plane at that point that crosses the article and is orthogonal to thelongitudinal axis of the article. The “longitudinal axis” of an articleis the axis along the largest dimension of the article. Similarly, a“longitudinal section” of an article is a portion of the article alongthe longitudinal axis of the article that can have any length greaterthan zero and less than or equal to the length of the article.Additionally, the “length” of an elongated article is a distance alongthe longitudinal axis from end to end of the article.

As used herein, a “cylindrical” article is an article having an exteriorshaped like a cylinder, but does not define or reflect any propertiesregarding the interior of the article. In other words, a cylindricalarticle may have a solid interior, may have a hollowed-out interior,etc. Generally, a cross-section of a cylindrical article appears to becircular or approximately circular, but other cross-sectional shapes arealso possible, such as a hexagonal shape. The cross-section may have anyarbitrary shape, including, but not limited to, square, rectangular, orelliptical. Regular and irregular shapes are also included.

As used herein, an “array” of articles (e.g., nanoscopic wires)comprises a plurality of the articles, for example, a series of alignednanoscale wires, which may or may not be in contact with each other. Asused herein, a “crossed array” or a “crossbar array” is an array whereat least one of the articles contacts either another of the articles ora signal node (e.g., an electrode).

As used herein, a “wire” generally refers to any material having aconductivity of or of similar magnitude to any semiconductor or anymetal, and in some embodiments may be used to connect two electroniccomponents such that they are in electronic communication with eachother. For example, the terms “electrically conductive” or a “conductor”or an “electrical conductor” when used with reference to a “conducting”wire or a nanoscale wire, refers to the ability of that wire to passcharge. Typically, an electrically conductive nanoscale wire will have aresistivity comparable to that of metal or semiconductor materials, andin some cases, the electrically conductive nanoscale wire may have lowerresistivities, for example, resistivities of less than about 100microOhm cm (μΩ cm). In some cases, the electrically conductivenanoscale wire will have a resistivity lower than about 10⁻³ ohm meters,lower than about 10⁻⁴ ohm meters, or lower than about 10⁻⁶ ohm meters or10⁻⁷ ohm meters.

A “semiconductor,” as used herein, is given its ordinary meaning in theart, i.e., an element having semiconductive or semi-metallic properties(i.e., between metallic and non-metallic properties). An example of asemiconductor is silicon. Other non-limiting examples include gallium,germanium, diamond (carbon), tin, selenium, tellurium, boron, orphosphorus.

A “nanoscopic wire” (also known herein as a “nanoscopic-scale wire” or“nanoscale wire”) generally is a wire, that at any point along itslength, has at least one cross-sectional dimension and, in someembodiments, two orthogonal cross-sectional dimensions less than 1micron, less than about 500 nm, less than about 200 nm, less than about150 nm, less than about 100 nm, less than about 70, less than about 50nm, less than about 20 nm, less than about 10 nm, or less than about 5nm. In other embodiments, the cross-sectional dimension can be less than2 nm or 1 nm. In one set of embodiments, the nanoscale wire has at leastone cross-sectional dimension ranging from 0.5 nm to 100 nm or 200 nm.In some cases, the nanoscale wire is electrically conductive. Wherenanoscale wires are described having, for example, a core and an outerregion, the above dimensions generally relate to those of the core. Thecross-section of a nanoscopic wire may be of any arbitrary shape,including, but not limited to, circular, square, rectangular, annular,polygonal, or elliptical, and may be a regular or an irregular shape.The nanoscale wire may be solid or hollow. A non-limiting list ofexamples of materials from which nanoscale wires of the invention can bemade appears below. Any nanoscale wire can be used in any of theembodiments described herein, including carbon nanotubes, molecularwires (i.e., wires formed of a single molecule), nanorods, nanowires,nanowhiskers, organic or inorganic conductive or semiconductingpolymers, and the like, unless otherwise specified. Other conductive orsemiconducting elements that may not be molecular wires, but are ofvarious small nanoscopic-scale dimensions, can also be used in someinstances, e.g. inorganic structures such as main group and metalatom-based wire-like silicon, transition metal-containing wires, galliumarsenide, gallium nitride, indium phosphide, germanium, cadmiumselenide, etc. A wide variety of these and other nanoscale wires can begrown on and/or applied to surfaces in patterns useful for electronicdevices in a manner similar to techniques described herein involving thespecific nanoscale wires used as examples, without undueexperimentation. The nanoscale wires, in some cases, may be formedhaving dimensions of at least about 1 micron, at least about 3 microns,at least about 5 microns, or at least about 10 microns or about 20microns in length, and can be less than about 100 nm, less than about 80nm, less than about 60 nm, less than about 40 nm, less than about 20 nm,less than about 10 nm, or less than about 5 nm in thickness (height andwidth). The nanoscale wires may have an aspect ratio (length tothickness) of greater than about 2:1, greater than about 3:1, greaterthan about 4:1, greater than about 5:1, greater than about 10:1, greaterthan about 25:1, greater than about 50:1, greater than about 75:1,greater than about 100:1, greater than about 150:1, greater than about250:1, greater than about 500:1, greater than about 750:1, or greaterthan about 1000:1 or more in some cases.

A “nanowire” (e. g. comprising silicon and/or another semiconductormaterial, such as an elemental semiconductor) is a nanoscopic wire thatis typically a solid wire, and may be elongated in some cases.Preferably, a nanowire (which is abbreviated herein as “NW”) is anelongated semiconductor, i.e., a nanoscale semiconductor. A“non-nanotube nanowire” is any nanowire that is not a nanotube. In oneset of embodiments of the invention, a non-nanotube nanowire having anunmodified surface (not including an auxiliary reaction entity notinherent in the nanotube in the environment in which it is positioned)is used in any arrangement of the invention described herein in which ananowire or nanotube can be used.

As used herein, a “nanotube” (e.g. a carbon nanotube) is a nanoscopicwire that is hollow, or that has a hollowed-out core, including thosenanotubes known to those of ordinary skill in the art. “Nanotube” isabbreviated herein as “NT.” Nanotubes are used as one example of smallwires for use in the invention and, in certain embodiments, devices ofthe invention include wires of scale commensurate with nanotubes.Examples of nanotubes that may be used in the present invention include,but are not limited to, single-walled nanotubes (SWNTs). Structurally,SWNTs are formed of a single graphene sheet rolled into a seamless tube.Depending on the diameter and helicity, SWNTs can behave asone-dimensional metals and/or semiconductors. SWNTs. Methods ofmanufacture of nanotubes, including SWNTs, and characterization areknown. Methods of selective functionalization on the ends and/or sidesof nanotubes also are known, and the present invention makes use ofthese capabilities for molecular electronics in certain embodiments.Multi-walled nanotubes are well known, and can be used as well.

Examples of nanotubes that may be used in the present invention includesingle-walled nanotubes (SWNTs) that exhibit unique electronic and/orchemical properties that are particularly suitable for molecularelectronics. Structurally, SWNTs are formed of a single graphene sheetrolled into a seamless tube with a diameter on the order of about 0.5 nmto about 5 nm and a length that can exceed about 10 microns. Dependingon diameter and helicity, SWNTs can behave as one-dimensional metals orsemiconductor and are currently available as a mixture of metallic andsemiconducting nanotubes. Methods of manufacture of nanotubes, includingSWNTs, and characterization are known. Methods of selectivefunctionalization on the ends and/or sides of nanotubes also are known,and the present invention makes use of these capabilities for molecularelectronics. The basic structural/electronic properties of nanotubes canbe used to create connections or input/output signals, and nanotubeshave a size consistent with molecular scale architecture. Those ofordinary skill in the art will know of methods of preparing nanotubes.See, for example, Kong, et al., “Synthesis of Individual Single-WalledCarbon Nanotubes on Patterned Silicon Wafers,” Nature, 395:878-881(1998); or Kong, et al., “Chemical Vapor Deposition of Methane forSingle-Walled Carbon Nanotubes,” Chem. Phys. Lett., 292:567-574 (1998).

Certain nanoscale wires of the present invention are individualnanoscale wires. As used herein, “individual nanoscale wires” means ananoscale wire free of contact with another nanoscale wire (but notexcluding contact of a type that may be desired between individualnanoscale wires in a crossbar array). For example, an “individual” or a“free-standing” article may, at some point in its life, not be attachedto another article, for example, with another nanoscopic wire, or thefree-standing article may be in solution. Such a free-standing articlemay be, for instance, removed from the location where it is made, as anindividual article, and transported to a different location and combinedwith different components to make a functional device such as thosedescribed herein and those that would be contemplated by those ofordinary skill in the art upon reading this disclosure. This is incontrast to conductive portions of articles which differ fromsurrounding material only by having been altered chemically orphysically, in situ, i.e., where a portion of a uniform article is madedifferent from its surroundings by selective doping, etching, etc.

In some cases, the nanoscale wire may comprise inorganic structures suchas Group IV, Group III/Group V, Group II/Group VI elements, transitiongroup elements, or the like, as described herein. For example, thenanoscale wires may be made of semiconducting materials such as silicon,indium phosphide, gallium nitride and others. The nanoscale wires mayalso include, for example, any organic, inorganic molecules that arepolarizable or have multiple charge states. For example,nanoscopic-scale structures may include main group and metal atom-basedwire-like silicon, transition metal-containing wires, gallium arsenide,gallium nitride, indium phosphide, germanium, or cadmium selenidestructures. In one set of embodiments, the nanoscale wire includes ametal-semiconductor compound.

The nanoscale wires may include various combinations of materials,including semiconductors and dopants. The following arenon-comprehensive examples of materials that may be used as dopants. Forexample, the dopant and/or the nanoscale wire may be an elementalsemiconductor, for example, silicon, germanium, tin, selenium,tellurium, boron, diamond, or phosphorus. The dopant may also be a solidsolution of various elemental semiconductors. Examples include a mixtureof boron and carbon, a mixture of boron and P(BP₆), a mixture of boronand silicon, a mixture of silicon and carbon, a mixture of silicon andgermanium, a mixture of silicon and tin, or a mixture of germanium andtin.

In some embodiments, the dopant and/or the semiconductor may includemixtures of Group IV elements, for example, a mixture of silicon andcarbon, or a mixture of silicon and germanium. In other embodiments, thedopant or the semiconductor may include a mixture of a Group III and aGroup V element, for example, BN, BP, BAs, AlN, AlP, AlAs, AlSb, GaN,GaP, GaAs, GaSb, InN, InP, InAs, or InSb. Mixtures of these may also beused, for example, a mixture of BN/BP/BAs, or BN/AlP. In otherembodiments, the dopants may include alloys of Group III and Group Velements. For example, the alloys may include a mixture of AlGaN, GaPAs,InPAs, GaInN, AlGaInN, GaInAsP, or the like. In other embodiments, thedopants may also include a mixture of Group II and Group VIsemiconductors. For example, the semiconductor may include ZnO, ZnS,ZnSe, ZnTe, CdS, CdSe, CdTe, HgS, HgSe, HgTe, BeS, BeSe, BeTe, MgS,MgSe, or the like. Alloys or mixtures of these dopants are also bepossible, for example, (ZnCd)Se, or Zn(SSe), or the like. Additionally,alloys of different groups of semiconductors may also be possible, forexample, a combination of a Group II-Group VI and a Group III-Group Vsemiconductor, for example, (GaAs)_(x)(ZnS)_(1-x). Other examples ofdopants may include combinations of Group IV and Group VI elements, suchas GeS, GeSe, GeTe, SnS, SnSe, SnTe, PbO, PbS, PbSe, or PbTe. Othersemiconductor mixtures may include a combination of a Group I and aGroup VII, such as CuF, CuCl, CuBr, CuI, AgF, AgCl, AgBr, AgI, or thelike. Other dopant compounds may include different mixtures of theseelements, such as BeSiN₂, CaCN₂, ZnGeP₂, CdSnAs₂, ZnSnSb₂, CuGeP₃,CuSi₂P₃, Si₃N₄, Ge₃N₄, Al₂O₃, (Al,Ga,In)₂(S,Se,Te)₃, Al₂CO,(Cu,Ag)(Al,Ga,In,Tl,Fe)(S,Se,Te)₂ and the like.

For Group IV dopant materials, a p-type dopant may be selected fromGroup III, and an n-type dopant may be selected from Group V, forexample. For silicon semiconductor materials, a p-type &pant may beselected from the group consisting of B, Al and In, and an n-type dopantmay be selected from the group consisting of P, As and Sb. For GroupIII-Group V semiconductor materials, a p-type dopant may be selectedfrom Group II, including Mg, Zn, Cd and Hg, or Group IV, including C andSi. An n-type dopant may be selected from the group consisting of Si,Ge, Sn, S, Se and Te. It will be understood that the invention is notlimited to these dopants, but may include other elements, alloys, ormaterials as well.

As used herein, the term “Group,” with reference to the Periodic Table,is given its usual definition as understood by one of ordinary skill inthe art. For instance, the Group II elements include Mg and Ca, as wellas the Group II transition elements, such as Zn, Cd, and Hg. Similarly,the Group III elements include B, Al, Ga, In and Tl; the Group IVelements include C, Si, Ge, Sn, and Pb; the Group V elements include N,P, As, Sb and Bi; and the Group VI elements include O, S, Se, Te and Po.Combinations involving more than one element from each Group are alsopossible. For example, a Group II-VI material may include at least oneelement from Group II and at least one element from Group VI, e.g., ZnS,ZnSe, ZnSSe, ZnCdS, CdS, or CdSe. Similarly, a Group III-V material mayinclude at least one element from Group III and at least one elementfrom Group V, for example GaAs, GaP, GaAsP, InAs, InP, AlGaAs, or InAsP.Other dopants may also be included with these materials and combinationsthereof, for example, transition metals such as Fe, Co, Te, Au, and thelike. The nanoscale wire of the present invention may further include,in some cases, any organic or inorganic molecules. In some cases, theorganic or inorganic molecules are polarizable and/or have multiplecharge states.

As used herein, transition metal groups of the periodic table, whenreferred to in isolation (i.e., without referring to the main groupelements), are indicated with a “B.” The transition metals elementsinclude the Group IB elements (Cu, Ag, Au), the Group IIB elements (Zn,Cd, Hg), the Group IIIB elements (Sc, Y, lanthanides, actinides), theGroup IVB elements (Ti, Zr, Hf), the Group VB elements (V, Nb, Ta), theGroup VIB elements (Cr, Mo, W), the Group VIIB elements (Mn, Tc, Re),and the Group VIIIB elements (Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, Pt).

In some embodiments, at least a portion of a nanoscopic wire may be abulk-doped semiconductor. As used herein, a “bulk-doped” article (e. g.an article, or a section or region of an article) is an article forwhich a dopant is incorporated substantially throughout the crystallinelattice of the article, as opposed to an article in which a dopant isonly incorporated in particular regions of the crystal lattice at theatomic scale, for example, only on the surface or exterior. For example,some articles such as carbon nanotubes are typically doped after thebase material is grown, and thus the dopant only extends a finitedistance from the surface or exterior into the interior of thecrystalline lattice. It should be understood that “bulk-doped” does notdefine or reflect a concentration or amount of doping in asemiconductor, nor does it necessarily indicate that the doping isuniform. In particular, in some embodiments, a bulk-doped semiconductormay comprise two or more bulk-doped regions. Thus, as used herein todescribe nanoscopic wires, “doped” refers to bulk-doped nanoscopicwires, and, accordingly, a “doped nanoscopic (or nanoscale) wire” is abulk-doped nanoscopic wire. “Heavily doped” and “lightly doped” areterms the meanings of which are understood by those of ordinary skill inthe art.

A bulk-doped semiconductor may include various combinations ofmaterials, including other semiconductors and dopants. In one set ofembodiments, the nanoscale wire may comprise a semiconductor that isdoped with an appropriate dopant to create an n-type or p-typesemiconductor as desired. For example, silicon may be doped with boron,aluminum, phosphorus, or arsenic. Laser catalytic growth may be used tointroduce controllably the dopants during the vapor phase growth ofsilicon nanoscale wires. Controlled doping of nanoscale wires can becarried out to form, e.g., n-type or p-type semiconductors. Dopantsincluding, but not limited to, zinc, cadmium, or magnesium can be usedto form p-type semiconductors, and dopants including, but not limitedto, tellurium, sulfur, selenium, or germanium can be used as dopants toform n-type semiconductors. These materials define direct band gapsemiconductor materials and these and doped silicon are well known tothose of ordinary skill in the art. The present invention contemplatesuse of any doped silicon or direct band gap semiconductor materials fora variety of uses, as discussed above. Examples of doped semiconductorscan be seen in U.S. patent application Ser. No. 09/935,776, filed Aug.22, 2001, entitled “Doped Elongated Semiconductors, Growing SuchSemiconductors, Devices Including Such Semiconductors, and FabricatingSuch Devices,” by Lieber, et al., published as U.S. Patent ApplicationPublication No. 2002/0130311 on Sep. 19, 2002; or U.S. patentapplication Ser. No. 10/196,337, filed Jul. 16, 2002, entitled“Nanoscale Wires and Related Devices,” by Lieber, et al., published asU.S. Patent Application Publication No. 2003/0089899 on May 15, 2003;each incorporated herein by reference.

The invention provides, as previously described, a nanoscale wire orwires forming part of a system constructed and arranged to determine ananalyte in a sample to which the nanoscale wire(s) is exposed.

The term “sample” refers to any cell, tissue, or fluid from a biologicalsource (a “biological sample”), or any other medium, biological ornon-biological, that can be evaluated in accordance with the inventionincluding, such as serum or water. The sample may be contained in afluid, e.g., in solution. A sample includes, but is not limited to, abiological sample drawn from an organism (e.g. a human, a non-humanmammal, an invertebrate, a plant, a fungus, an algae, a bacteria, avirus, etc.), a sample drawn from food designed for human consumption, asample including food designed for animal consumption such as livestockfeed, milk, an organ donation sample, a sample of blood destined for ablood supply, a sample from a water supply, or the like.

A “sample suspected of containing” a particular component means a samplewith respect to which the content of the component is unknown. “Sample”in this context includes naturally-occurring samples, such asphysiological samples from humans or other animals, samples from food,livestock feed, etc. Typical samples taken from humans or other animalsinclude tissue biopsies, cells, whole blood, serum or other bloodfractions, urine, ocular fluid, saliva, or fluid or other samples fromtonsils, lymph nodes, needle biopsies, etc.

A variety of sample sizes, for exposure of a sample to a nanoscalesensor of the invention, can be used in various embodiments. Asexamples, the sample size used in nanoscale sensors may be less than orequal to about 10 microliters, less than or equal to about 1 microliter,or less than or equal to about 0.1 microliter. The sample size may be assmall as about 10 nanoliters, 1 nanoliter, or less, in certaininstances. The nanoscale sensor also allows for unique accessibility tobiological species and may be used for in vivo and/or in vitroapplications. When used in vivo, in some case, the nanoscale sensor andcorresponding method result in a minimally invasive procedure.

“Determine,” as used herein, generally refers to the analysis of a stateor condition, for example, quantitatively or qualitatively. For example,a species, or an electrical state of a system may be determined.“Determining” may also refer to the analysis of an interaction betweentwo or more species, for example, quantitatively or qualitatively,and/or by detecting the presence or absence of the interaction, e.g.determination of the binding between two species. As an example, ananalyte may cause a determinable change in an electrical property of ananoscale wire (e.g., electrical conductivity, resistivity, impedance,etc.), a change in an optical property of the nanoscale wire, etc.Examples of determination techniques include, but are not limited to,conductance measurement, current measurement, voltage measurement,resistance measurement, piezoelectric measurement, electrochemicalmeasurement, electromagnetic measurement, photodetection, mechanicalmeasurement, acoustic measurement, gravimetric measurement, and thelike. “Determining” also means detecting or quantifying interactionbetween species.

As used herein, the term “reaction entity” refers to any entity that caninteract with an analyte in such a manner as to cause a detectablechange in a property of a nanoscale wire. The reaction entity maycomprise a binding partner to which the analyte binds. The reactionentity, when a binding partner, can comprise a specific binding partnerof the analyte. In some cases, the reaction entity can form a coating onthe nanoscale wire. Non-limiting examples of reaction entities include anucleic acid (e.g., DNA or RNA), an antibody, a sugar or a carbohydrate,a protein or an enzyme, a ganglioside or a surfactant, etc., e.g., asdiscussed herein.

In one set of embodiments, a reaction entity associated with thenanoscale wire is able to interact with an analyte. The reaction entity,as “associated” with or “immobilized” relative to the nanoscale wire,may be positioned in relation to the nanoscale wire (e.g., in closeproximity or in contact) such that the analyte can be determined bydetermining a change in a characteristic or property of the nanoscalewire. Interaction of the analyte with the reaction entity may cause adetectable change or modulation in a property of the nanoscale wire, forexample, through electrical coupling with the reaction entity. Forexample, interaction of an analyte with a reaction entity may bedetermined by determining a change in an electrical property of thenanoscale wire, for example, voltage, current, conductivity,resistivity, inductance, impedance, electrical change, anelectromagnetic change, etc.

As used herein, a component that is “immobilized relative to” anothercomponent either is fastened to the other component or is indirectlyfastened to the other component, e.g., by being fastened to a thirdcomponent to which the other component also is fastened. For example, afirst entity is immobilized relative to a second entity if a speciesfastened to the surface of the first entity attaches to an entity, and aspecies on the surface of the second entity attaches to the same entity,where the entity can be a single entity, a complex entity of multiplespecies, another particle, etc. In certain embodiments, a component thatis immobilized relative to another component is immobilized using bondsthat are stable, for example, in solution or suspension. In someembodiments, non-specific binding of a component to another component,where the components may easily separate due to solvent or thermaleffects, is not preferred.

As used herein, “fastened to or adapted to be fastened to,” as used inthe context of a species relative to another species or a speciesrelative to a surface of an article (such as a nanoscale wire), or to asurface of an article relative to another surface, means that thespecies and/or surfaces are chemically or biochemically linked to oradapted to be linked to, respectively, each other via covalentattachment, attachment via specific biological binding (e.g.,biotin/streptavidin), coordinative bonding such as chelate/metalbinding, or the like. For example, “fastened” in this context includesmultiple chemical linkages, multiple chemical/biological linkages, etc.,including, but not limited to, a binding species such as a peptidesynthesized on a nanoscale wire, a binding species specificallybiologically coupled to an antibody which is bound to a protein such asprotein A, which is attached to a nanoscale wire, a binding species thatforms a part of a molecule, which in turn is specifically biologicallybound to a binding partner covalently fastened to a surface of ananoscale wire, etc. A species also is adapted to be fastened to asurface if a surface carries a particular nucleotide sequence, and thespecies includes a complementary nucleotide sequence.

“Specifically fastened” or “adapted to be specifically fastened” means aspecies is chemically or biochemically linked to or adapted to be linkedto, respectively, another specimen or to a surface as described abovewith respect to the definition of “fastened to or adapted to befastened,” but excluding essentially all non-specific binding.“Covalently fastened” means fastened via essentially nothing other thanone or more covalent bonds.

As used herein, “attached to,” in the context of a species relative toanother species or to a surface of an article, means that the species ischemically or biochemically linked via covalent attachment, attachmentvia specific biological binding (e.g., biotin/streptavidin),coordinative bonding such as chelate/metal binding, or the like. Forexample, “attached” in this context includes multiple chemical linkages,multiple chemical/biological linkages, etc., for example, a bindingspecies such as a peptide synthesized on a polystyrene bead. “Covalentlyattached” means attached via one or more covalent bonds.

The term “binding” refers to the interaction between a correspondingpair of molecules or surfaces that exhibit mutual affinity or bindingcapacity, typically due to specific or non-specific binding orinteraction, including, but not limited to, biochemical, physiological,and/or chemical interactions. “Biological binding” defines a type ofinteraction that occurs between pairs of molecules including proteins,nucleic acids, glycoproteins, carbohydrates, hormones, and the like.Specific non-limiting examples include antibody/antigen,antibody/hapten, enzyme/substrate, enzyme/inhibitor, enzyme/cofactor,binding protein/substrate, carrier protein/substrate,lectin/carbohydrate, receptor/hormone, receptor/effector, complementarystrands of nucleic acid, protein/nucleic acid repressor/inducer,ligand/cell surface receptor, virus/ligand, virus/cell surface receptor,etc.

The term “binding partner” refers to a molecule that can undergo bindingwith a particular molecule. Biological binding partners are examples.For example, Protein A is a binding partner of the biological moleculeIgG, and vice versa. Other non-limiting examples include nucleicacid-nucleic acid binding, nucleic acid-protein binding, protein-proteinbinding, enzyme-substrate binding, receptor-ligand binding,receptor-hormone binding, antibody-antigen binding, etc. Bindingpartners include specific, semi-specific, and non-specific bindingpartners as known to those of ordinary skill in the art. For example,Protein A is usually regarded as a “non-specific” or semi-specificbinder. The term “specifically binds,” when referring to a bindingpartner (e.g., protein, nucleic acid, antibody, etc.), refers to areaction that is determinative of the presence and/or identity of one orother member of the binding pair in a mixture of heterogeneous molecules(e.g., proteins and other biologics). Thus, for example, in the case ofa receptor/ligand binding pair the ligand would specifically and/orpreferentially select its receptor from a complex mixture of molecules,or vice versa. An enzyme would specifically bind to its substrate, anucleic acid would specifically bind to its complement, an antibodywould specifically bind to its antigen. Other examples include nucleicacids that specifically bind (hybridize) to their complement, antibodiesspecifically bind to their antigen, binding pairs such as thosedescribed above, and the like. The binding may be by one or more of avariety of mechanisms including, but not limited to ionic interactions,and/or covalent interactions, and/or hydrophobic interactions, and/orvan der Waals interactions, etc.

The following documents are incorporated herein by reference in theirentirety for all purposes, and include additional description ofteachings usable with the present invention: U.S. Provisional PatentApplication Ser. No. 60/142,216, filed Jul. 2, 1999, entitled “MolecularWire-Based Devices and Methods of Their Manufacture,” by Lieber, et al.;International Patent Application No. PCT/US00/18138, filed Jun. 30,2000, entitled “Nanoscopic Wire-Based Devices, Arrays, and Methods ofTheir Manufacture,” by Lieber, et al., published as WO 01/03208 on Jan.11, 2001; U.S. Provisional Patent Application Ser. No. 60/226,835, filedAug. 22, 2000, entitled “Semiconductor Nanowires,” by Lieber, et al.;U.S. Provisional Patent Application Ser. No. 60/254,745, filed Dec. 11,2000, entitled “Nanowire and Nanotube Nanosensors,” by Lieber, et al.;U.S. Provisional Patent Application Ser. 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The following examples are intended to illustrate certain embodiments ofthe present invention, but do not exemplify the full scope of theinvention.

EXAMPLE 1

In this example, a nanowire field effect transistor was prepared, onwhich a PNA sequence was immobilized onto a portion of the nanowire forsingle DNA molecule detection.

In FIG. 2A, silicon nanowire 20 was synthesized by chemical vapordeposition using 10 nm gold nanoparticles as the catalyst particles,silane as reactant, and diborane as a p-type dopant, with a Si:B ratioof 4000:1. A device 40 comprising a silicon nanowire field effecttransistor (FET) was fabricated using photolithography, with a definedchannel length of about 2 micrometers and 50 nm of nickel evaporated oneach end of nanowire 20 to make contacts 25. After lift-off, device 40was pre-annealed at 380° C. in H₂/N₂ forming gas for 90 seconds. Thendevice 40 was annealed again at 415° C. to facilitate diffusion ofnickel and formation of nickel silicide along the silicon nanowire(i.e., to define a first portion of the nanowire 21) (FIG. 2B). For a 10nm diameter silicon nanowire, 40 seconds of annealing at 415° C.resulted in a channel length (i.e., a second portion of the nanowire 22)of less than about 100 nm (FIG. 2C), as shown in the SEM image of aspecific device with a ˜70 nm channel (FIG. 2D).

Next, the device 40 was exposed to aldehyde propyltrimethoxysilane or3-mercaptopropyltrimethoxysilane (2% silane in ethanol) for 60 minutes(FIG. 2E and FIG. 2J). The silane reacted with the silicon oxide surfaceon the second portions of the nanowire 22 and can generally give amonolayer of the function group within 60 minutes. After exposure to thesilane and rinse with ethanol thoroughly, the device 40 was baked at120° C. in N₂ for 10 minutes. Then, device 40 was incubated with 20microliters of a 30 micromolar Lys-O-PNA sequence (for the aldehydesilane surface), with 4 mM NaBH₃CN in 10 mM phosphate buffer at a pH of8.3 overnight, or a MCC-OO-PNA sequence (i.e., a maleimide-linker-PNAmoiety for the thiol silane surface) in 10 mM phosphate buffer at a pH 7for 4 hours, resulting in immobilization of the PNA sequence relative tothe second portion of the nanowire 22 (FIG. 2F). The unreacted aldehydegroups were blocked by incubation with ethanolamine in the presence of 4mM NaBH₃CN in 10 mM phosphate buffer. The PNA sequence used in thisexample was ATCATCTTTG (SEQ ID NO: 1), but other PNA sequences can beused as well. Additionally, other surface chemistry can also be used toimmobilize the PNA sequence, for example, as is shown in FIGS. 2D-2F,e.g., involving epoxide ring opening reactions (FIG. 2I).

Device 40 could then be used as a sensor, e.g., if the nanowire FET isgated by charged molecules. For instance, as discussed in the belowexamples, by exposing the PNA sequence to a substantially complementaryDNA sequence (e.g., 1 nanomolar DNA in 10 micromolar PBS), associationof the DNA sequence to the PNA sequence may be determined (FIG. 2G).(See FIG. 2K, illustrating the electronic circuit of the FET.)

EXAMPLE 2

In this example, the nanoscale sensor device fabricated in Example 1(having the PNA binding partner described in that example) was used todetermine DNA analytes in a solution. The PNA sequence was ATCATCTTTG(SEQ ID NO: 1) with the N-terminus attached to the nanowire surface. Thebuffer solutions used in all measurements was 10 micromolar PBS. The DNAsequences were dissolved in the same buffer solution. Two DNA sequencesused in this example were TTTTTTTTTT (SEQ ID NO: 6) (“poly(T)₁₀”) andATCAAAGATG (SEQ ID NO: 5). The DNA sequence ATCAAAGATG (SEQ ID NO: 5)was expected to hybridize with the PNA through the IS interaction of 8base pairs, i.e. the CAAAGATG (SEQ ID NO: 7) of the DNA to the CATCTTTG(SEQ ID NO: 8) sequence of the PNA. The AC amplitude through thenanowire in this example was 30 mV and the frequency was 17 Hz.

FIG. 3A illustrates the conductance (in nanosiemens) vs. time (inseconds) data recorded for the PNA-modified p-type silicon nanowireafter sequentially delivery of the following solutions: buffer, 1 nMpoly(T)₁₀, buffer, 1 nM ATCAAAGATG (SEQ ID NO: 5), buffer, 10 nMATCAAAGATG (SEQ ID NO: 5), and buffer. No measurable conductance signalwas observed in both the buffer and 1 nM poly(T)₁₀ solutions. However,upon flowing matched DNA sequence ATCAAAGATG (SEQ ID NO: 5), one DNAmolecule appeared to hybridize with one PNA molecule on the nanowire, asshown in FIG. 3A. It is believed that the negative charges on the DNAmolecule produces positive image charges in the nanowire, so theconductance of the p-type nanowire jumped to a higher value, which wasdetermined in real time and indicated by the arrows in FIG. 3A. When theDNA dehybridizes and leaves the nanowire surface, the conductance of thenanowire jumped back to the original value. This behavior (repeatedbinding/unbinding of DNA) continued while the DNA solution was passedover the nanowires used in this example.

FIG. 3B and FIG. 3C illustrate detailed time trajectories for the 1 nMand 10 nM DNA solutions. From each of these time trajectories, the dwelltimes with DNA on and off the PNA probe could be determined, which couldbe used to determine unbinding and binding rate of the DNA molecules tothe PNA probes on the nanowire surface, as shown in FIG. 3D-3G. In thesefigures, N_(on)(t) or N_(off)(t) represents the number of events withdwell times of the “on” or “off” state shorter than time t, which couldthen be used to determine the unbinding or binding rate constants (i.e.,dissociation/association rate constants). The grey lines in thesefigures are the single-exponential fit of the processes, which gavek_(off)(1 nM)=0.0065 s⁻¹ (FIG. 3D), k_(on)(1 nM)=0.022 s⁻¹ (FIG. 3E),k_(off)(10 nM)=0.0068 s⁻¹ (FIG. 3F), and k_(on)(10 nM)=0.14 s⁻¹ (FIG.3G) respectively. It was found in this example that the unbinding rateconstants were similar for 1 nM and 10 nM DNA solutions, i.e., 0.0065s⁻¹ and 0.0068 s⁻¹, respectively. However for the binding process, therate constant for the 10 nM DNA solution was about 6.4 times greaterthan for the 1 nM DNA solution.

This example demonstrates the ability to detect specifically the singlemolecule binding and unbinding events onto a silicon nanowire surface,and to measure the concentration dependent binding and unbinding rateconstants of the hybridization between DNA and PNA e.g., to determinethe concentration of the DNA in the solution.

EXAMPLE 3

In this example, the nanoscale sensor fabricated in Example 1 (havingthe PNA binding partner described in that example) was used todiscriminate mismatched DNA and perfectly matched DNA sequences at thesingle molecule level. In this example, three types of DNA were used:perfectly complementary DNA, having a sequence CAAAGATGAT (SEQ ID NO:2), or substantially complementary DNA that was not perfectlycomplementary, but having 1 or 2 mismatches, CAAACATGAT (SEQ ID NO: 3)or CAAACCTGAT (SEQ ID NO: 4), respectively. The DNA were all atconcentration of 100 nM. The AC amplitude through the nanowires in thisexample was 20 mV and the frequency was 509 Hz.

FIGS. 4A-4C are plots of conductance (in nS) with respect to time (in s)for solutions containing DNA with a single mismatch in the middle, DNAwith two mismatches in the middle, and perfectly complementary DNA. Bymeasuring the dwell times of the “on” and “off” states as in Example 2,the rate constants of binding and unbinding (i.e.,association/dissociation) were determined for a single mismatched DNAand double mismatched DNA. (FIGS. 4C and 4D for k_(off) and k_(on) forFIG. 4A, respectively, and FIGS. 4E and 4F for k_(off) and k_(on) forFIG. 4B, respectively). Note that FIGS. 4A-4C only show the portions ofthe experiments where the nanowires were exposed to DNA. Curve-fittingof these data yielded, for a single mismatch, k_(on)=1.67 s⁻¹ andk_(off)=0.166 s⁻¹, and for a double mismatch, k_(on)=1.20 s⁻¹ andk_(off)=14.80 s⁻¹. Thus, while the binding rate constants werecomparable for single and double mismatched sequences, the unbindingrate constants were markedly different, indicating that the doublemismatch was approximately 90 times more easily to leave than the singlemismatch. Further, no dissociation appeared to have occurred between theperfectly complementary DNA and its PNA binding partner during theexperiment (>2000 s).

This example thus demonstrates the ability to both discriminatesingle-point mutation in DNA sequences and reveal the underlyingbiophysical relevance of binding and unbinding steps.

EXAMPLE 4

This example illustrates that, according to certain embodiments of theinvention, a nanowire may be used to detect multiple binding orassociation of individual DNA molecules.

A nanowire was prepared using techniques similar to those described inExample 1, on which a portion of the nanowire a PNA sequence wasimmobilized. The PNA sequence was ATCATCTTTG (SEQ ID NO: 1). The PNA wasexposed to DNA having a sequence CAAAGATGAT (SEQ ID NO: 2), i.e.,perfectly complementary DNA. The conductance vs. time data is shown inFIG. 5. In this figure, the conductance increases by discrete “steps,”which each correspond to individual binding events between one DNAmolecule and one PNA molecule on the nanowire surface. It should benoted that no unbinding was detected between the PNA and the perfectlycomplementary DNA.

EXAMPLE 5

In this example, with reference to FIG. 7, the sensitivity of nanoscalewires used in certain embodiments of the invention are illustrated.However, this theoretical discussion is presented by way of illustrationonly, and should not be construed as being limiting in any way.

FIG. 7 shows a nanoscale wire, used in a FET, having a contactresistances R_(s) (source) and R_(d) (drain). R_(c), the total contactresistance, is:R _(c) =R _(s) +R _(d).

Within the wire itself, R₁ and R₂ are the resistances of the portions ofthe nanoscale wire (portions having lengths l₁ and l₂, respectively)that are not “gated” or altered upon binding of the analyte to thenanoscale wire (e.g., to a binding partner immobilized relative to thenanoscale wire). Under the diffusion limit (e.g., in a siliconnanowire):R ₁ +R ₂ =r(l ₁ +l ₂),where r is the resistivity per unit length of the nanoscale wire.

R_(g) can be defined as the resistance of the portion of the nanoscalewire that is gated (altered) upon binding of one analyte molecule.Defining R_(g) ⁰ as the resistance, before binding, and R_(g) ¹ as theresistance after binding, then the difference is:R _(g) ¹ =R _(g) ⁰ −ΔR _(g),where ΔR_(g) is the resistance change. The resistance change may bedetermined, e.g., by the charge and/or size of the analyte (e.g., ofDNA), electronic properties of the nanoscale wire, and/or the distancebetween the analyte and the nanoscale wire. In the treatment in thisexample, this value can be treated as a constant for a given analyte,nanoscale wire, and surface chemistry of the device.

This yields a conductance change, ΔG, of:

$\begin{matrix}{{\Delta\; G} = {\frac{1}{R_{c} + {r\left( {l_{1} + l_{2}} \right)} + R_{g}^{0} - {\Delta\; R_{g}}} - \frac{1}{R_{c} + {r\left( {l_{1} + l_{2}} \right)} + R_{g}^{0}}}} \\{= {\frac{\Delta\; R_{g}}{\left\lbrack {R_{c} + {r\left( {l_{1} + l_{2}} \right)} + R_{g}^{0} - {\Delta\; R_{g}}} \right\rbrack\left\lbrack {R_{c} + {r\left( {l_{1} + l_{2}} \right)} + R_{g}^{0}} \right\rbrack}.}}\end{matrix}$

Thus, as R_(c) decreases, the conductance change signal increases, andas the length (l₁+l₂) decreases, the conductance change signalincreases. Also, good electronic properties of the nanowire, e.g. highmobility, and good surface chemistry can give a relatively high ΔR_(g)and a relatively high ΔG. Thus, better contacts, shorter lengths, and/orgood nanomaterial and surface chemistries may yield highersensitivities, i.e., ΔG.

While several embodiments of the present invention have been describedand illustrated herein, those of ordinary skill in the art will readilyenvision a variety of other means and/or structures for performing thefunctions and/or obtaining the results and/or one or more of theadvantages described herein, and each of such variations and/ormodifications is deemed to be within the scope of the present invention.More generally, those skilled in the art will readily appreciate thatall parameters, dimensions, materials, and configurations describedherein are meant to be exemplary and that the actual parameters,dimensions, materials, and/or configurations will depend upon thespecific application or applications for which the teachings of thepresent invention is/are used. Those skilled in the art will recognize,or be able to ascertain using no more than routine experimentation, manyequivalents to the specific embodiments of the invention describedherein. It is, therefore, to be understood that the foregoingembodiments are presented by way of example only and that, within thescope of the appended claims and equivalents thereto, the invention maybe practiced otherwise than as specifically described and claimed. Thepresent invention is directed to each individual feature, system,article, material, kit, and/or method described herein. In addition, anycombination of two or more such features, systems, articles, materials,kits, and/or methods, if such features, systems, articles, materials,kits, and/or methods are not mutually inconsistent, is included withinthe scope of the present invention.

All definitions, as defined and used herein, should be understood tocontrol over dictionary definitions, definitions in documentsincorporated by reference, and/or ordinary meanings of the definedterms.

The indefinite articles “a” and “an,” as used herein in thespecification and in the claims, unless clearly indicated to thecontrary, should be understood to mean “at least one.”

The phrase “and/or,” as used herein in the specification and in theclaims, should be understood to mean “either or both” of the elements soconjoined, i.e., elements that are conjunctively present in some casesand disjunctively present in other cases. Multiple elements listed with“and/or” should be construed in the same fashion, i.e., “one or more” ofthe elements so conjoined. Other elements may optionally be presentother than the elements specifically identified by the “and/or” clause,whether related or unrelated to those elements specifically identified.Thus, as a non-limiting example, a reference to “A and/or B”, when usedin conjunction with open-ended language such as “comprising” can refer,in one embodiment, to A only (optionally including elements other thanB); in another embodiment, to B only (optionally including elementsother than A); in yet another embodiment, to both A and B (optionallyincluding other elements); etc.

As used herein in the specification and in the claims, “or” should beunderstood to have the same meaning as “and/or” as defined above. Forexample, when separating items in a list, “or” or “and/or” shall beinterpreted as being inclusive, i.e., the inclusion to of at least one,but also including more than one, of a number or list of elements, and,optionally, additional unlisted items. Only terms clearly indicated tothe contrary, such as “only one of” or “exactly one of,” or, when usedin the claims, “consisting of,” will refer to the inclusion of exactlyone element of a number or list of elements. In general, the term “or”as used herein shall only be interpreted as indicating exclusivealternatives (i.e. “one or the other but not both”) when preceded byterms of exclusivity, such as “either,” “one of,” “only one of,” or“exactly one of.” “Consisting essentially of,” when used in the claims,shall have its ordinary meaning as used in the field of patent law.

As used herein in the specification and in the claims, the phrase “atleast one,” in reference to a list of one or more elements, should beunderstood to mean at least one element selected from any one or more ofthe elements in the list of elements, but not necessarily including atleast one of each and every element specifically listed within the listof elements and not excluding any combinations of elements in the listof elements. This definition also allows that elements may optionally bepresent other than the elements specifically identified within the listof elements to which the phrase “at least one” refers, whether relatedor unrelated to those elements specifically identified. Thus, as anon-limiting example, “at least one of A and B” (or, equivalently, “atleast one of A or B,” or, equivalently “at least one of A and/or B”) canrefer, in one embodiment, to at least one, optionally including morethan one, A, with no B present (and optionally including elements otherthan B); in another embodiment, to at least one, optionally includingmore than one, B, with no A present (and optionally including elementsother than A); in yet another embodiment, to at least one, optionallyincluding more than one, A, and at least one, optionally including morethan one, B (and optionally including other elements); etc.

It should also be understood that, unless clearly indicated to thecontrary, in any methods claimed herein that include more than one stepor act, the order of the steps or acts of the method is not necessarilylimited to the order in which the steps or acts of the method arerecited.

In the claims, as well as in the specification above, all transitionalphrases such as “comprising,” “including,” “carrying,” “having,”“containing,” “involving,” “holding,” “composed of,” and the like are tobe understood to be open-ended, i.e., to mean including but not limitedto. Only the transitional phrases “consisting of” and “consistingessentially of” shall be closed or semi-closed transitional phrases,respectively, as set forth in the United States Patent Office Manual ofPatent Examining Procedures, Section 2111.03.

What is claimed is:
 1. An article, comprising: a nanoscale wirecomprising a first portion and a second portion laterally defined alongthe length of the nanoscale wire, the first portion consistingessentially of a single crystal of a transition metal silicide compound,the compound being stoichiometric, and the second portion comprising asemiconductor, having a length of less than 100 nm, and havingimmobilized relative thereto a binding partner of an analyte, whereinthe first portion is free of the binding partner.
 2. The article ofclaim 1, wherein the transition metal comprises nickel.
 3. The articleof claim 1, wherein the nanoscale wire is part of a FET.
 4. The articleof claim 1, wherein the nanoscale wire further comprises a third portionbeing defined laterally along the nanowire, the second portionseparating the first portion and the third portion, the third portionconsisting essentially of a single crystal of the transitionmetal-semiconductor compound.
 5. The article of claim 1, wherein thesecond portion has a length of less than 50 nm.
 6. The article of claim1, wherein the second portion has a length of less than 30 nm.
 7. Thearticle of claim 1, wherein the second portion further comprises abinding partner to an analyte immobilized relative thereto.
 8. Thearticle of claim 7, wherein the analyte is a nucleic acid.
 9. Thearticle of claim 7, wherein the binding partner is a nucleic acid. 10.The article of claim 7, wherein the article comprises a plurality ofnanoscale wires, each comprising distinguishable nucleic acidsimmobilized relative thereto.
 11. An article, comprising: a sampleexposure region able to hold a solution containing an analyte; ananoscale wire positioned at least partially adjacent to or within thesample exposure region, the nanoscale wire comprising a first portionand a second portion, each laterally defined along the nanoscale wire,the second portion comprising a semiconductor and having immobilizedrelative thereto a binding partner able to bind to the analyte containedin the solution, and the first portion being free of the binding partnerand comprising a conductive transition metal silicide compound, thecompound being stoichiometric, wherein the binding partner is able tobind one or more molecules of the analyte, wherein the analyte, whenbound to the binding partner, has a Debye screening length within thesolution that is greater than the greatest dimension of the secondportion of the nanoscale wire.
 12. The article of claim 11, wherein theanalyte comprises a nucleic acid.
 13. The article of claim 11, wherein asingle molecule of the analyte, when bound to the binding partner, has aDebye screening length than the greatest dimension of the second portionof the nanoscale wire.
 14. The article of claim 11, wherein thetransition metal silicide compound consists essentially of a singlecrystal.
 15. The article of claim 11, wherein the nanoscale wirecomprises the first portion, the second portion, and a third portioneach laterally defined along the nanoscale wire, wherein the thirdportion is free of the binding partner and comprises a conductivetransition metal-semiconductor compound.